Abstract
The two neutral non-ketonic steroids of pregnant mare''s urine (compounds MN and MM of Brooks et al. 1952) are identified as the 5[alpha]-androstane-3[beta]:16[alpha]- (and -3[beta]:16[beta]-)diols. The constitution of "uranolone" (Marker et al. 1938b) is confirmed as 17[alpha][beta]-hydroxy-17[alpha]-methyl-5[alpha]-D-homoandrostan-3-one. Species differences in urinary steroids between the human female and the mare are discussed.