dissenting:

I.

The Great Writ of habeas corpus is not a very popular instrument these days. Surprisingly, it is the federal judiciary which appears to find the use of the writ increasingly distasteful. A habeas corpus petitioner must cross a field filled with procedural landmines before the merits of his claims may be heard in federal court: exhaustion of remedies, procedural default, abuse of the writ, etc. Often he must do so without the help of a lawyer because there is no right to counsel on collateral attack, even though fundamental constitutional rights are ordinarily at stake. The various doctrinal obstacles provide abundant opportunities for state officials to foreclose any decision on the merits of the habe-as application simply by resorting to proce *1329 dural arguments. The states’ attorneys handling habeas cases are presumably well-trained and skilled litigators who possess, or at the very least ought to be charged with, detailed knowledge of the governing law. They usually have all the advantages on their side when they litigate against a habeas petitioner. It is difficult for me to understand why, under these circumstances, when states’ attorneys fail to raise the appropriate legal arguments in a given ease, the courts should excuse the very types of failures that we are unwilling to excuse when the petitioner is the party in default. After all, ours is supposed to be an adversary and even handed-system of justice. If it truly is, it should not only be the petitioner who forfeits his rights when he fails to raise them in a timely manner. 1

In this case, the state of Idaho failed to challenge petitioner James Woolery’s contention that the rule of Stone v. Powell, 428 U.S. 465 , 96 S.Ct. 3037 , 49 L.Ed.2d 1067 (1976), did not bar consideration of his Fourth Amendment claims on collateral review. In his pretrial brief Woolery specifically stated that “[t]he key issue” before the court was whether he had been “provided with an opportunity for full and fair litigation of his fourth amendment claim.” 2 Woolery asserted that he had not, and at no time did the state allege or argue otherwise. Respondent prevailed on the merits of Woolery’s claim before the magistrate judge to whom Wool-ery’s petition had been referred under 28 U.S.C. section 636 (b). 3 Idaho did not object to the district judge’s consideration of the merits of Woolery’s petition until long after he had rejected the magistrate judge’s recommendation and granted'Woolery’s habeas corpus application. Only on appeal did the state change its legal position and contend, for the first time, that consideration of the merits of Woolery’s petition was barred by Stone v. Powell. 4 It also argued, without citing any supporting authority, that Stone requires a district court to make a determination whether a petitioner has received a full and fair opportunity to litigate his Fourth Amendment claims in state court even where the state has not asserted that he did. ‘

By excusing Idaho from what was either incompetent representation or an ill-advised litigation strategy and by accepting respondent’s novel interpretation of Stone v. Powell, the majority, in effect, creates for the benefit of states’ attorneys an unwarranted and unprecedented exception from the rule that district courts are under no obligation to raise non-jurisdictional issues sua sponte. 5 In doing so, my colleagues misconstrue the theoretical basis for the Supreme Court’s decision in Stone . Additionally, the majority’s decision conflicts with the approach taken by all *1330 the other circuits that have considered the question and ignores a number of our own precedents. My colleagues neglect to explain why a state’s failure to invoke the Stone doctrine should be treated any differently from its failure to raise a petitioner’s procedural default, which our case law holds may be forfeited unless timely raised. The end result of all this is that the majority erroneously permits the state to foreclose judicial review of the merits of Woolery’s habeas petition.

II.

As the majority acknowledges, Stone’s “full and fair litigation” rule is not in any' sense jurisdictional. E.g., Withrow v. Williams, — U.S. —, —, 113 S.Ct. 1745, 1750 , 123 L.Ed.2d 407 (1993). Instead, it rests on concerns of prudence and equity. Id.; id. — U.S. at—, 113 S.Ct. at 1757 (O’Connor, J., concurring in part and dissenting in part); id. — U.S. at—, 113 S.Ct. at 1767 (Scalia, J., concurring in part and dissenting in part). Habeas corpus relief is itself equitable in nature. The decision whether to grant the writ in a particular instance depends upon a number of factors including: the benefit of relief to the petitioner, the reliability of the judgment under attack, federalism, finality, and the effective utilization of scarce federal judicial resources. See Withrow, — U.S. at—, 113 S.Ct. at 1750 . Based upon its weighing of these factors, the Stone v. Powell Court determined that a federal district court in its equitable discretion ought to refuse to entertain a ha-beas petition alleging a violation of the Fourth Amendment unless the petitioner did not receive a full and fair hearing in state court on that claim.

While the majority formally recognizes the proposition that Stone is not jurisdictional, it nevertheless rules that a federal district court is absolutely precluded from considering a petitioner’s Fourth Amendment claims unless it first finds that he did not receive a full and fair hearing. Indeed, the majority holds that a district court must raise the full and fair hearing issue sua sponte. I am aware of no other non-jurisdictional defect that must be raised by a district court on its own accord; in fact, the rule is settled that a district court is under no obligation to raise an issue sua sponte unless it relates to subject matter jurisdiction. See, e.g., Valenzuela v. Kraft, Inc., 801 F.2d 1170, 1172-73 (9th Cir.1986) (if timely filing of action is jurisdictional then district court must raise issue sua sponte; if not, then lack of timeliness may be waived by non-assertion) amended 815 F.2d 570 (9th Cir.1987). As a result, in all but name, the majority has transformed Stone v. Powell’s principle of equitable discretion into a jurisdictional prerequisite.

The majority’s holding conflicts with the approaches of three other circuits. The Seventh Circuit has held that a court need not raise Stone v. Powell sua sponte. Wallace v. Duckworth, 778 F.2d 1215 , 1220 n. 1 (7th Cir.1985). While the majority cites the Fifth Circuit’s decision in Davis v. Blackburn, 803 F.2d 1371 (5th Cir.1986) (per curiam), as being in “accord” with its own, Davis is actually in conflict with it. There, a divided panel of the Fifth Circuit held that an appellate court may raise Stone v. Powell sua sponte. 6 It did not hold that a district court was required to do so. As the First Circuit noted in a case in which it reached the merits of a Fourth Amendment habeas claim in part because the state had failed to raise Stone in the district court, Davis is based on the exercise of discretion. Tart v. Massachusetts, 949 F.2d 490 , 497 n. 6 (1st Cir.1991). If, as the majority concludes, states really were incapable of forfeiting Stone v. Powell and district courts were mandated to raise it on their own, then federal appellate courts would be required to raise the bar themselves in every case. In other words, either Stone categorically prohibits a federal court from entertaining a habeas petition where the lack of a full and fair hearing has not been shown or it provides only a basis for the exercise of discretionary authority when equitable considerations so dictate. Three circuits have taken the latter approach; only the majority has endorsed the former.

*1331 The majority attempts to justify its “categorical limitation” on the basis of language in footnote 37 of Stone v. Powell that a petitioner must show the lack of a full and fair hearing. 7 428 U.S. at 494 n. 37, 96 S.Ct. at 3052 n. 37. Although that footnote is somewhat unclear and therefore susceptible to an overly broad reading, it simply does not answer the question before us and the majority’s reliance on it is misplaced. Nothing in footnote 37 suggests that where, as here, a petitioner claims that his hearing was not full and fair, and the state fails to argue otherwise, a district judge cannot decide that the state has conceded the point and reach the merits of the petition. The footnote nowhere implies that a district court must raise Stone v. Powell sua sponte. The question whether a state must raise Stone is distinct from the one footnote 37 answers — that a petitioner must show the lack of full and fair hearing once the issue is raised by the state.

The law of procedural defaults clearly demonstrates the error that underlies the majority’s overreading of footnote 37. Like Stone v. Powell the procedural default doctrine is based upon equitable principles. Withrow , — U.S. at—, 113 S.Ct. at 1757 (O’Connor, J., concurring and dissenting). In language remarkably similar to that found in footnote 37 the Court has held:

Coleman v. Thompson, — U.S.—,—, 111 S.Ct. 2546, 2565 , 115 L.Ed.2d 640 (1991) (emphasis added). While the burden of showing “cause and prejudice” is on the petitioner, it is absolutely clear that if the state fails to raise the doctrine of procedural default, a federal court may reach the merits of a habeas application. See Jenkins v. Anderson, 447 U.S. 231 , 234 n. 1, 100 S.Ct. 2124 , 2127 n. 1, 65 L.Ed.2d 86 (1980); Suniga v. Bunnell, 998 F.2d 664, 667 (9th Cir.1993). The reason is simple: The equities that normally weigh against consideration of a procedurally defaulted claim, finality and federalism, do not have equivalent force where a state has not asserted an interest in compliance with its own procedural rules in the petitioner’s federal habeas corpus proceedings. See Harmon v. Ryan, 959 F.2d 1457, 1461 (9th Cir.1992). Thus, if a state does not raise the. procedural default issue in the district court, it may forfeit it on appeal.

Similarly, finality and federalism do not justify a rule requiring federal courts to refuse to hear Fourth Amendment claims where a state fails to assert its interest in the integrity of its own prior adjudication of them. Concerns of federalism and respect for a state’s criminal judgment are marginal where a state commits a procedural forfeiture. Boardman v. Estelle, 957 F.2d 1523, 1537 (9th Cir.) (per curiam), cert. denied, — U.S. —, 113 S.Ct. 297 , 121 L.Ed.2d 221 (1992). Comity does not require a court to be the state’s advocate. Davis v. Blackburn, 803 F.2d at 1375 (Rubin, J., dissenting). The majority simply fails to acknowledge that its blanket exemption of state forfeitures in Fourth Amendment cases cannot be reconciled with our procedural default law.

At bottom, the Stone v. Powell rule is a derivative of issue preclusion principles. See Withrow v. Williams, — U.S. at— — —, 113 S.Ct. at 1767-68 (Scalia, J., concurring and dissenting) (tracing history of full and fair litigation principle). Ordinarily, if a party has already prevailed in the litigation of an issue on a prior occasion but does not raise the potentially preclusive effect of the previous determination, a court has no obligation to raise collateral estoppel sua sponte. Compare Moore v. City of Paducah, 890 F.2d 831 , 833 n. 4 (6th Cir.1989) (under Fed. R.Civ.P. 8(c) collateral estoppel must be pled *1332 or it will be deemed waived) 8 with McCain v. Apodaca, 793 F.2d 1031 , 1032-34 & n. 2 (9th Cir.1986) (a court is permitted to raise preclusion doctrines sua sponte); accord Alyeska Pipeline Serv. Co. v. United States, 688 F.2d 765, 771 , 231 Ct.Cl. 540 (1982) (a court may, when necessary, raise claim or issue preclusion sua sponte although primary purpose of rule is for protection of adverse party), cert. denied 461 U.S. 943 , 103 S.Ct. 2120 , 77 L.Ed.2d 1301 (1983); see also Charles Alan Wright et al., 13 Federal Practice and Procedure, § 4405, 32-33 (1981) (both claim and issue preclusion may be waived by party entitled to demand preclusion). A state that fails to argue that a habeas petitioner’s Fourth Amendment claim was fully and fairly litigated in state court is not entitled to an exemption from the rule that preclusion is an argument that can be forfeited.

Assuming for the sake of argument that the majority is correct that Stone v. Powell is a categorical limitation on the authority of district courts to consider claims of Fourth Amendment violation occurring in state prosecutions — and I believe it clearly is not— such a conclusion would still not prevent a forfeiture by Idaho. Such limitations are treated differently from jurisdictional limitations. 9 In Martinez v. Ylst, 951 F.2d 1153, 1156-57 (9th Cir.1991), we decided that the state could forfeit the argument that a petitioner’s claim was non-constitutional and therefore not cognizable on habeas corpus. There is no question that a court has “no authority” to grant habeas relief for non-constitutional trial errors. See 28 U.S.C. §§ 2241 (c) & 2254(a). However, in Martinez we did not conclude that this fact compelled the adoption of a special rule for the state’s benefit. There, we treated the state like any other litigant and held that by litigating the error as a constitutional one in the trial court and by failing to raise a contrary view until its reply brief in the court of appeals, it had forfeited its argument that the error was non-constitutional. That the state failed to raise the relevant argument in its opening brief as well as in the district court in Martinez does not meaningfully distinguish that case from the instant one. Martinez shows that an argument that a case does not fall within the class of claims cognizable on habe-as can be forfeited through a failure to raise it. Martinez’s reasoning is controlling here and the majority’s decision that Stone v. Powell cannot be forfeited is in conflict.

In short, if a state does not assert an interest in the finality of its own proceedings, it forfeits its right to insist that federal courts not consider a particular habeas petition. That is as true with respect to Fourth Amendment claims as with all others. A federal court is not required to raise Stone v. Powell sua sponte. It may choose to do so or it may, in the exercise of its equitable discretion, reach the merits of a habeas application alleging a deprivation of Fourth Amendment rights. The majority’s imposition of a duty upon district courts to raise the preclusive effect of a prior state proceeding is simply unwarranted under precedent, general principles of habeas corpus, or the rules of procedure.

III.

While a federal appellate court, like a district court, is permitted to raise Stone v. Powell on its own, I would not do so as a general matter, nor would I do so in the instant case. See Davis v. Blackburn, 803 F.2d at 1373-75 (Rubin, J., dissenting). It is our standard practice, except in limited circumstances, not to consider issues that the parties fail to raise in the district court, and I see no reason to depart from that policy with state forfeitures in Fourth Amendment cases. Where a violation of constitutional rights has been claimed, a federal court should not ordinarily remedy the procedural failures of the alleged constitutional violator and thereby prevent consideration of those claims on the merits. That is especially true in a case such as this one where the petitioner’s claims of constitutional deprivation are meritorious.

*1333 In Granberry v. Greer, 481 U.S. 129 , 107 S.Ct. 1671 , 95 L.Ed.2d 119 (1987), the Supreme Court held that federal appellate courts may choose to consider a state’s argument that a habeas petitioner’s claims are not properly exhausted, even if the argument was not raised before the district court. The Court explicitly rejected the state’s position that a federal appellate court must consider such arguments. Id. at 131-33 , 107 S.Ct. at 1673-74 . Granberry holds that appellate courts should decide on a case by case basis whether to hear non-exhaustion arguments not presented below. Id. at 134-36 , 107 S.Ct. at 1675-76 . However, cases involving a state’s failure to raise a Stone v. Powell objection call for a less lenient and less flexible standard.

Granberry clearly assumed that a petitioner could present any non-exhausted claims to a state court after the initial dismissal of his federal habeas application and that he could thereafter obtain federal review. See id. at 134-35 , 107 S.Ct. at 1675 . However, the consequences of addressing a non-exhaustion claim are quite different from those that usually follow from a state’s invocation of Stone v. Powell. In cases like the one before us, the result is most often outright dismissal of a petition with no further opportunity for consideration of the merits by any court. Given the basic principle that we ought to decide eases on their merits, I believe that we should presumptively decline to consider a Stone v. Powell argument when it is raised for the first time on appeal. Accordingly, I would treat Idaho’s failure to argue that Woolery’s claim is barred by Stone as a forfeiture.

IV.

On the merits, the district court correctly determined that under our decision in United States v. Harvey, 701 F.2d 800, 803-06 (9th Cir.1983), the seizure of Woolery’s blood without his consent was in violation of his Fourth Amendment rights because he had not been formally placed under arrest. The district judge properly rejected the magistrate judge’s conclusion that Harvey was undermined by Skinner v. Labor Executives’ Ass’n, 489 U.S. 602 , 109 S.Ct. 1402 , 103 L.Ed.2d 639 (1989). Skinner permits a state to have a program of requiring employees to undergo urinalysis after accidents. This case involves suspicion that a particular individual was intoxicated. Skinner rested in part on the fact that uniform and standardized investigations pose far less of a threat to Fourth Amendment rights and present less of a danger of overreaching by law enforcement than do intrusions based upon individualized circumstances. 489 U.S. at 621 , 109 S.Ct. at 1415 ; see also United States v. Martinez-Fuente, 428 U.S. 543, 559 , 96 S.Ct. 3074, 3083 , 49 L.Ed.2d 1116 (1975) (routine stop of all vehicles to check for undocumented aliens mitigates possible abuse of discretion by officers) Moreover, the searches at issue in Skinner did not involve the actual drawing of fluids, in distinction to the search that occurred in Harvey and in the present case. Skinner, 489 U.S. at 625-26 , 109 S.Ct. at 1417-18 . Drawing blood is a physically invasive procedure; requiring a urine sample is not. As the district court correctly determined, Harvey is controlling.

Because the state forfeited its interest in the preclusive effect of the prior détermination of Woolery’s Fourth Amendment claim by not raising Stone v. Powell before either the magistrate judge or the district judge, I would reach the merits of his petition and decide them in Woolery’s favor. Accordingly, I would affirm the judgment of the district court.

. For example, a state habeas petitioner who files his appeal three days late forfeits his right to have his claims heard in federal court, even when he is facing execution and among his claims is one that he is innocent. Coleman v. Thompson, - U.S. -, 111 S.Ct. 2546 , 115 L.Ed.2d 640 (1991).

. Although Woolery alleged the lack of a full and fair hearing in his pre-trial brief rather than in his habeas petition, the state does not argue that this technical error is of any significance and has thus forfeited the argument. The state's contention that Woolery’s brief was somehow deficient for using the phrase "fair consideration" rather than "full and fair litigation” is not only incorrect (he used both terms) but is contrary to the rule that pro se litigants are not held to the standards of technical proficiency that are imposed upon members of the bar. Given the circumstances of this appeal, the state's criticisms of the adequacy of Woolery's submissions in the district court are particularly inappropriate.

. Because of the state's failure to address the Stone v. Powell issue, the magistrate judge refused to decide Woolery's petition on that ground.

. While the rule in this circuit is that a party may pursue in the court of appeals claims of legal error by a magistrate judge even where no objection was raised in the district court, Barilla v. Ervin, 886 F.2d 1514, 1518 (9th Cir.1986), that principle is not dispositive here. In this case, the state failed to raise the relevant issue before the magistrate judge or the district court.

. The majority’s decision is ironic in light of the holding of another panel of this court that civil rights plaintiffs who fail to cite the relevant qualified immunity cases to the district court forfeit their right to have the court of appeals correct the judge's legal errors. Elder v. Holloway, 951 F.2d 1112 (9th Cir.1991), amended 975 F.2d 1388 (9th Cir.1992), cert. granted,-U.S.-, 113 S.Ct. 3033 , 125 L.Ed.2d 721 (1993). Given the disparity in resources between civil rights plaintiffs and states’ attorneys, the double standard is particularly surprising.

. For the reasons set forth in Judge Rubin’s persuasive dissent, I think the Davis majority erred in raising Stone v. Powell on its own, but that is another matter. See infra section III.

. The magistrate judge imprecisely described the Stone v. Powell bar as an "affirmative defense”. While footnote 37 shows that this description is technically incorrect, Idaho never objected in the district court to the magistrate judge's terminology or his decision to rule on the merits of Wool-ery's claims.

. Under Rule 11 of the Rules Governing Habeas Corpus, the Federal Rules of Civil Procedure may be applied on habeas corpus to the extent that they are not inconsistent with the Rules Governing Habeas Corpus.

. As is demonstrated supra, 1) the limitation here is not jurisdictional and 2) only where the issue is jurisdictional are the federal courts required to raise the question of their right to proceed sua sponte.