In a search for inhibitors of 17 alpha-hydroxylase-C17,20-lyase and testosterone-5 alpha-reductase, target enzymes in the development of drugs to treat hormone-dependent prostatic cancer, we have identified certain compounds chemically derived by the hydrolysis of decafluoroazobenzene (4) as novel inhibitors for these two enzymes. Hydrolysis of 4 gave the known 4-hydroxynonafluoroazobenzene (1) and the novel 2-hydroxynonafluoroazobenzene (2). By AlI3 demethylation of 4,4'-dimethoxyoctafluoroazobenzene (5) or by hydrolysis of 4 under phase-transfer conditions 4,4'-dihydroxyoctafluoroazobenzene (3) was obtained. Compounds 1 and 2 were inhibitors of the hydroxylase (IC50 values, respectively, 30 and 63 microM) and of the lyase (IC50 values 33 and 16 microM) steps on the pathway of androgen biosynthesis. The 2-hydroxy compound 2 underwent spontaneous conversion into octafluorodibenz[b,f][1,4,5]oxadiazepine (6) which had IC50 values, respectively, of 50 and 15 microM for the hydroxylase and lyase steps and which contributed to the observed activity of 2. Effective inhibitors of the 5 alpha-reductase were 1 (Ki 10 microM) and 3 (Ki4 microM): the activities of 1 and 3 were markedly pH dependent, with respective IC50 values of 14 and 5 microM at pH 7.4 and of 2 and 0.8 microM at pH 6.6.