Defendants’ constitutional challenge to the inference authorized by 21 U.S.C. § 174 as applied to heroin cases is disposed of by Turner v. United States, 396 U.S. 398 , 90 S.Ct. 642 , 24 L.Ed.2d 610 (January 20, 1970).

We agree with defendants, however, that prejudicial error occurred in instructing the jury regarding the inference.

The jury was informed that the “explanation of possession to the satisfaction of the jury,” referred to in section 174, was an explanation of “innocent” possession. This is not the law. Even if the defendant’s possession of narcotic drugs is unlawful, the jury is to acquit if there is reasonable doubt either that the drugs were imported contrary to law or that the defendant knew they were unlawfully imported. United States v. Peeples, 377 F.2d 205, 209 (2d Cir. 1967); United States v. Llanes, 374 F.2d 712, 715-716 (2d Cir. 1967); Chavez v. United States, 343 F.2d 85, 88-90 (9th Cir. 1965); Griego v. United States, 298 F.2d 845, 848-849 (10th Cir. 1962). 1

More important, the instructions left the impression that if possesion were proved beyond a reasonable doubt, conviction should follow; they obscured the fact that the ultimate burden remained with the government to prove each element of the offense beyond a reasonable doubt. For example, the jury was instructed that “proof of possession, unless satisfactorily explained, avoids the necessity of the Government proving both the illegal importation and the defend *789 ant’s knowledge thereof” (emphasis added). But there was no clear instruction that defendants were to be acquitted unless, upon all the evidence including proof of possession, the jury was satisfied beyond a reasonable doubt thát the heroin was unlawfully imported and defendants had knowledge of that fact. 2 See, in addition to cases cited above, Turner v. United States, 396 U.S. 398, 405-407 , 90 S.Ct. 642, 646-647 (January 20, 1970); Verdugo v. United States, 402 F.2d 599, 603 (9th Cir. 1968); United States v. Glaziou, 402 F.2d 8, 17 (2d Cir. 1968).

Reversed and remanded.

. “An explanation of possession ‘to the satisfaction of the jury, as those words are used in the second paragraph of § 174, means any evidence, direct or circumstantial, which is sufficient to satisfy the jury that despite evidence of possession by the defendant the government has failed to meet its burden of proof. Such a failure of proof may occur, despite proof of possession, witli respect to any one of the essential elements of the § 174 offense.” Verdugo v. United States, 402 F.2d 599, 601 , 603 n. 3 (9th Cir. 1968).

. The following instruction, requested by both defendants, was refused: