Abstract
19‐Hydroxy‐prostaglandin B1, isolated from human seminal plasma, was treated with tritiumlabeled acetic anhydride and degraded by oxidation with permanganate in acetone. Tritiumlabeled 3‐acetoxybutanoic acid was isolated from the oxidation product and diluted with unlabeled dl‐3‐acetoxybutanoic acid. The morphine salt of the acid was resolved. These experiments showed that the tritium‐labeled 3‐acetoxybutanoic acid had the d‐configuration and consequently the parent 19‐hydroxy‐prostaglandin B1 has the d‐configuration at C‐19. The configuration at C‐15 is discussed.