The contribution of adrenal androgens to the maintenance and progression of so‐called hormone‐unresponsive prostatic carcinoma was studied in 20 patients with advanced relapsed disease. The role played by testicular androgens had been negated by prior orchiectomy or concurrent LHRH analogue therapy. Ketoconazole, an antifungal agent which inhibits adrenal and testicular androgenesis, administered in a dose of 400 mg 8‐hourly, resulted in optimal suppression of adrenal androgens. The mean serum androstenedione concentration fell from 8.01 ± 0.84 nMol/l to 1.55 ± 0.25 nMol/l, P < 0.001, and serum testosterone from 1.25 ± 0.14 nMol/l to 0.36 ± 0.06 nMol/l, P <0.01, after 6 months treatment. There was, however, no significant difference between patients receiving 400 and those receiving 200 mg. Androgen suppression resulted in six objective and ten subjective clinical responses. Ablation of both testicular and adrenal androgens can now be achieved using ketoconazole in combination with orchiectomy or LHRH analogues, but the high incidence of side effects may preclude its use in all patients with prostatic cancer. The results of this study support the concept of “total androgen ablation” as primary therapy in advanced prostatic cancer as a possible means of improving survival in this common malignancy.