Human skin biotransform naturally occurring steroid hormones. 4-14C progesterone skin fate might involve C-19 derivates formation. In vitro incubation of 4-14C-progesterone with defammation. human abdominal skin minces for 5 days periods, predominantly yield: 1) Metabolites reduced at C-20 and C-5 positions of 4-14C progesterone. 2) 4-pregnen-17 01-20-one (0.85%). 3) 4-Androsten-17-01-3-one isolated as an acetylated derivative (0.29%). 4) A metabolite that behaves like 4-androsten-3, 17-diol. The metabolites identity was established through repeated cocrystallizations with known purified carriers in different organic solvents 17 -hydroxy-progesterone was found at greater concentrations in the group of polar metabolites. These metabolites are of biochemical interest but can not be assessed until the effects of these compounds on human skin are known.