The testes obtained at surgery from a 15-yr-old “female” patient were incubated with testosterone-4-14C, androst-4- ene-3,17-dione-4-14C and progesterone-4-14C. The neutral lipide fraction (with the aid of carrier steroids) on fractionation and purification by conventional methods, including chromatography on partition columns, paper and thin layer and formation of derivatives, yielded the following radiochemically pure substances: androst-4-ene-3,17-dione, testosterone, 6β-hydroxy testosterone, 16α-hydroxyprogesterone and 17α-hydroxyprogesterone. The phenolic fraction contained estrone, 17β- estradiol and equilenin. The data indicate that the feminizing testicular tissue possesses aromatizing enzymes as well as a very active 16α-hydroxylase. (Endocrinology76: 966, 1965)