Two of 14 patients with Cushing's syndrome treated on a long-term basis with ketoconazole developed sustained hypertension. In both cases normal plasma and urinary free cortisol levels had been achieved following ketoconazole therapy, yet continuous blood pressure monitoring demonstrated hypertension 31 (patient 1) and 52 weeks (patient 2) after treatment. In patient 1, plasma levels of deoxycorticosterone and 11-deoxycortisol were elevated. In patient 2, in addition to an increase in both deoxycorticosterone and 11-deoxycortisol levels, plasma aldosterone values were raised, with a concomitant suppression of renin levels. Our findings show that long-term treatment with high doses of ketoconazole may induce enzyme blockade leading to mineralocorticoid-related hypertension.