Homogenates from human myometrium with an added NADPH regenerating system and ATP were incubated with 4-(14)C progesterone. Six metabolites were identified: 5alpha-pregnane-3, 20-dione, 5beta-pregnane-3, 20-dione, 3alpha-hydroxy-4-pregnen-20-one, 3beta hydroxy-4-pregnen-20-one. 20alpha-hydroxy-4-pregnen-3-one and 20beta-hydroxy-4-pregnen-3-one. The identification of these metabolites was based on their behaviour in paper and thin layer chromatography and especially in radiogaschromatography either as free compounds or after formation of derivatives. The identification of the two allylic metabolites was supplemented by specific microchemical and enzymatic reactions. The formation of 5beta-pregnane-3, 20-dione, 20beta-hydroxy-4-pregnen-3-one and of the two allylic alcohols 3alpha-hydroxy-4-pregnen-20-one and 3beta-hydroxy-4-pregnen-20-one in human myometrium homogenates was demonstrated for the first time.