Incubation of the 1000 x g supernatant obtained from 23-day-old rat ovarian homogenate with labeled progesterone resulted in the production of 3 major metabolites; 5alpha-androstane-3alpha,17beta-diol, and two 5alpha-reduced pregnanes that were identified as 3alpha-hydroxy-5alpha-pregnan-20-one and 3alpha,17alpha-dihydroxy-5alpha-pregnan-20-one. The 3alpha,17alpha-dihydroxy-5alpha-pregnan-20-one has not been hitherto isolated from mammalian ovaries. The steroids were identified by their mobilities on thin-layer and gas-liquid chromatography, by mass spectroscopy, derivative formation and by recrystallization to constant specific activity. In another experiment, incubation of the 1000 x g supernatant from 23-day-old rat ovaries with 3alpha-hydroxy-5alpha-pregnan-20-one as substrate resulted in the production of 5alpha-androstane-3alpha,17beta-diol. It is suggested that 5alpha-androstane-3alpha,17beta-diol is produced in immature rat ovaries by a pathway in which the identified 5alpha-reduced pregnanes serve as intermediates.