Abstract Analogs of cholesterol and pregnenolone have been synthesized and tested as hormonal precursors. Homologues of cholesterol in which C-22 is completely substituted (e.g. (20R-20-t-butyl)-5-pregnene-3)β,20 diol, (20R)-20-(phenyl)-5-pregnene-3β,20 diol) were incubated with acetone powders of adrenal glands and appropriate cofactors and each was converted into pregnenolone. The side-chain fragment of the aryl derivative formed biosynthetically in this reaction was identified as phenol. In addition, another fragment, acetophenone, was isolated but the C 19-steroidal product of this unusual pathway has not yet been identified. In a comparable manner, the conversion of C 21-steroids into C 19-androgens was studied. An analog of pregnenolone which was devoid of oxygen at C-20, 5-pregnene-3β-ol, was synthesized and when incubated with testicular microsomes was converted into testosterone. These results suggest that the true intermediates in steroid biosynthesis may not be isolable hydroxylated compounds as traditionally conceived, but rather enzyme bound, transient, reactive species.