Urine was collected from a female pig-tail monkey (Macaca nemestrina) receiving intramuscular injections of [4-14C]progesterone (0·234μc, sp. act. 11·7 mμc/mg. in 1·0 ml. arachis oil) twice daily for 5 days. A fraction more polar than 5β-pregnane-3α,20α-diol was prepared by acid hydrolysis and chromatography on alumina (Jeffery, 1966). It was rechromatographed and a fraction containing 6-oxygenated metabolites of progesterone (James & Fotherby, 1965) was collected. On subsequent chromatograms, at least 70 % of the radioactive material in this fraction was found in a small region, regarded as the position of the main metabolite or its derivative. Paper chromatography and thin-layer chromatography (Table 1) showed that this metabolite behaved chromatographically like 3α,6α-dihydroxy-5β-pregnan-20-one. An aliquot (1670 disintegrations/min.) of the alumina column fraction was purified by thin-layer chromatography on silica gel GF (ethyl acetate: acetone, 4:1, v/v). Material eluted from the zone corresponding to 3α,6α-dihydroxy-5β-pregnan-20-one was chromatographed on paper (benzene: methanol: water, 10:7:3,