Charles Buschmann and a class consisting of himself and all present and future Supplemental Security Income (“SSI”) recipients in Region X appeal from a judgment of the district court upholding the validity of 20 C.F.R. § 416.1125 (d). 1 Buschmann raises two questions on appeal;

*355 The facts are not in dispute. Charles Buschmann had been receiving $42.30 a month in SSI benefits. He lived alone in a house owned by his son for which he paid $80 a month rent. The Secretary determined that the current market rental value of the dwelling was $145 a month. Under 20 C.F.R. 416.1125(d) this generated $65 a month of unearned income to Buschmann, thus terminating his continued eligibility for SSI benefits.

Buschmann filed a class action claiming (1) that the regulation exceeded the Secretary’s authority, and (2) that the regulation could not apply to any period prior to the date of its final publication. The district court granted the Secretary’s motion for summary judgment on these issues, but reversed the Secretary’s determination of current market rental value as not being supported by substantial evidence.

Buschmann appeals the district court’s decision. The Secretary does not appeal.

1. Validity of the Regulation

Buschmann argues that 20 C.F.R. § 416.1125 (d) violates SSI’s objective of guaranteeing minimum subsidies because the regulation counts as “income” savings that are not actually available to the recipients to meet their basic needs. This court upheld the validity of regulation 416.1125(d) in Antonioli v. Harris, 624 F.2d 78 (9th Cir. 1980):

Antonioli also disposes of Buschmann’s argument that the imputed income was unavailable to him:

Buschmann also claims that this regulation should be invalidated in that it is “arbitrary and capricious.” The decisions of Antionilo and Kimmes foreclose that claim. It should also be noted that the interpretation of an administrative regulation by the officers or agency charged with its administration is to be given controlling weight unless it is plainly erroneous or inconsistent with the regulation. Mourning v. Family Publications Service, Inc., 411 U.S. 356 , 93 S.Ct. 1652 , 36 L.Ed.2d 318 (1973); Udall v. Tallman, 380 U.S. 1 , 85 S.Ct. 792 , 13 L.Ed.2d 616 (1965); Bowles v. Seminole Rock Co., 325 U.S. 410 , 65 S.Ct. 1215 , 89 L.Ed. 1700 (1945). The interpretation of regulation 416.1125(d) is not plainly erroneous.

Thus we find that the assessment of in-kind support does not violate the purpose of the Social Security Act and is not arbitrary or capricious.

2. Noncompliance with the Administrative Procedures Act

A regulation is invalid if the agency fails to follow procedures required by the *356 Administrative Procedures Act, 5 U.S.C. § 553 . 4 U. S. Steel Corp. v. U. S. Environmental Protection, 595 F.2d 207, 210 (5th Cir. 1979); Anderson v. Butz, 550 F.2d 459, 462 (9th Cir. 1977); Hotch v. United States, 212 F.2d 280 (9th Cir. 1954); Carter v. Blum, 493 F.Supp. 368, 372 (S.D.N.Y.1980); Kelly v. United States Department of Interior, 339 F.Supp. 1095, 1100-1101 (E.D.Cal. 1972); City of New York v. Diamond, 379 F.Supp. 503, 518 (S.D.N.Y.1974).

Section 553(b) and (d) requires the agency to publish a substantive rule in the Federal Register no less than 30 days before the rule’s effective date, and to provide an opportunity for public comment. Section 553(b)(B) allows an exception “if the agency has ‘good cause’ to believe the process would ‘be impracticable, unnecessary, or contrary to the public interest’ and if the agency publishes reasons for thinking so along with the rules in question.” Western Oil & Gas v. United States E.P.A., 633 F.2d 803 , 810 (9th Cir. 1980). The Secretary did not comply with 5 U.S.C. § 553 when he proposed the presumed maximum value (PMV) now in dispute as an amendment to regulation 416.1125. Regulation 416.1125(d) was published for the first time in the Federal Register on January 29, 1974. It was preceded by the following preamble:

However, the PMV approach now in dispute was not published until October 20, 1975, when the Secretary published a proposed amendment to 416.1125. These new rules were given a limited retroactive effect:

The Secretary relies on the “good cause exception” in Section 553(b)(B) for the proposition that the agency could waive the 30-day notice rule. In order to avail itself of the “good cause exception” the agency must determine “that compliance with the 30-day requirement is either impracticable, unnecessary or contrary to the public interest.” Kelly v. United States Department of the Interior, supra, 339 F.Supp. at 1101 . It must then include this finding and a short statement of reasons with the new regulations. Id. The Secretary did not make such a finding in this case and did not include the reasons with the regulations he published on October 25, 1975.

The district court held that the preamble to the regulations published on January 29, 1974, indicated that all rules would be retroactive on publication because “the rule was designed to implement a statute which was in effect twenty-nine days earlier.” “Good cause” was the need to “administer the supplementary security income program” which was already in effect.

The district court’s analysis was too generous. The preamble of January 29, 1974, never mentioned the PMV approach adopted in October 1975. The PMV approach was a new method of calculating eligibility. The preamble does not mention any method of calculating eligibility. Furthermore, the Secretary made the disputed *357 provision of the amendment retroactive to December 1974 and not to the original effective date of January 1, 1974. The requirements of Section 553(b)(B) are clear. The finding and the reasons for waiving the 30-day notice must be published with the proposed rule. The preamble of January 29, 1974, cannot validate a rule published almost two years later.

The cases cited by the Secretary do not support the proposition that failure to comply with the requirements of § 553(b)(B) is insignificant. Nader v. Sawhill, 514 F.2d 1064, 1068 (Em.App.1975), and People of the State of California, State Lands Com’n v. Simon, 504 F.2d 430 (Em.App.1974), involve government price controls. The announcement of future controls could cause market distortions. U. S. Steel v. U. S. Environmental Protection, supra, 595 F.2d at 214, n.15 . No such exigency is involved here.

Other cases have indicated that the good cause exception should be interpreted narrowly, U. S. Steel Corp. v. U. S. Environmental Protection, supra, 595 F.2d at 214 ; Kelly v. United States Dept, of Interior, supra, 339 F.Supp. at 1102 , so that the exception will not swallow the rule. Nader v. Sawhill, supra, 514 F.2d at 1068 . The notice and comment procedure promotes public input into agency rulemaking:

The notice and comment procedures in Section 553 should be waived only when “delay would do real harm.” U. S. Steel v. U. S. Environmental Protection, supra, 595 F.2d at 214 . The good cause exception is essentially an emergency procedure. This court would not permit the Environmental Protection Agency to rely solely on statutory deadlines to satisfy the good cause exception in enacting clean air standards. Western Oil & Gas v. United States E.P.A., 633 F.2d 803 , 810-813 (9th Cir. 1980). Accord: State of N. J. v. U. S. Environmental Protection, 626 F.2d 1038 (D.C.Cir.1980); U. S. Steel Corp. v. United States Environmental Protection, supra, Sharon Steel Corp. v. Environmental Protection Agency, 597 F.2d 377 (3d Cir. 1979).

These procedural safeguards are just as important for social security recipients as they are for powerful corporations. There was no emergency that justified dispensing with the notice and comment procedure in this case. Certainly, the need to administer the supplemental security income program cannot satisfy the good cause exception. If the Secretary could waive the notice and comment procedure in this case, any agency *358 could waive Section 553 by saying that it was necessary to do so.

Title 5 U.S.C. § 706 provides that the court must take “due account” of the rule of “prejudicial error” in reviewing agency actions. The Secretary can rely on harmless error only “when a mistake of the administrative body is one that clearly had no bearing on the procedure used or the substance of decision reached.” (Citation omitted.) Braniff Airways v. C.A.B., 379 F.2d 453, 466 (D.C.Cir.1967), cited in U. S. Steel Corp. v. United States Environmental Protection, supra, 595 F.2d at 215 .

Applying this principle to this case is somewhat complicated. Plaintiffs and the Secretary agree that regulation 416.1125(d), published in final form on July 7, 1978, is valid and is identical to the interim regulation challenged in this case. The Secretary argues that his failure to follow the Administrative Procedures Act did not prejudice Buschmann or the class.

In light of the importance of the notice and comment procedure embodied in Section 553 and the failure to comply, we hold that the interim amendment to regulation 416.1125(d) (the PMV approach) was invalid from December 1974 until the promulgation of the final rule on July 7, 1978. We remand this case to the agency for recalculation of plaintiffs’ supplemental income benefits during that period.

The judgment is affirmed in part and reversed in part.

. 20 C.F.R. § 416.1125 (d) provides in pertinent part:

. 42 U.S.C. § 1382a(a)(2)(A) provides in pertinent part

. 5 U.S.C. § 553 provides:

. The Administrative Procedures Act is applicable to rulemaking by the Secretary of Health and Human Services. Although 5 U.S.C. § 553 (a)(2) would have exempted the rulemaking procedure now in dispute, the then Secretary of Health, Education and Welfare, in a policy statement dated January 28, 1971, ( 36 F.R. 2532 ), required all agencies and offices in his department to utilize the public participation procedures of § 553. The Secretary does not contest his legal obligation to comply with § 553 procedures.