The fungus Cephalosporium aphidicola has been shown to hydroxylate testosterone, 19-nortestosterone, 1-dehydrotestosterone, 1α-methyltestosterone, androst-4-en-3-one, androst-4-en-3,17-dione and 17α-methyltestosterone predominantly at the C-6β position with a minor hydroxylation occurring at the C-14α position. 19-Nortestosterone was also hydroxylated at the C-10β position. In contrast to the hydroxylation of progesterone by this organism, hydroxylation at C-11α was a minor pathway.