In the conversion of pregnenolone 1 into dehydroisoandrosterone 3 and 3-beta-hydroxyandrosta-5,16-diene 5 an atom of oxygen from O2 is incorporated into the side chain released as acetate; during the conversions the C-21 methyl hydrogens of the precursor are not disturbed, the status of 16-alpha and 17-alpha hydrogen atoms during the conversions is also defined.