Ketoconazole, an imidazole derivative which inhibits adrenal steroidogenesis, has been used with success for the metabolic control of Cushing's disease. Few data are available about the use of ketoconazole in the management of the ectopic ACTH syndrome. We have used ketoconazole in eight patients: four patients with Cushing's disease, two patients with overt and two with occult ectopic ACTH syndrome. Among patients with Cushing's disease, reversible hypoadrenalism occurred once. All had full clinical and biochemical regression of the disease for more than 6 months with 400-1200 mg ketoconazole per day. Patients with ectopic ACTH syndrome received 1200 mg ketoconazole per day for at least 2 months. Partial biochemical regression was observed in two and a secondary escape to adrenal blockade in two others. These findings further indicate that ketoconazole is a valuable tool for the metabolic control of Cushing's disease. On the contrary, in ectopic ACTH syndrome, this aim can be impossible to reach with ketoconazole although the reasons for its ineffectiveness remain to be determined.