We examined both activities and amounts of steroidogenic cytochrome P-450s at the posttranslational protein level and steroid contents in the adrenocortical adenoma from patients with primary aldosteronism and Cushing's syndrome. Aldosterone synthase cytochrome P-450 (human P-450aldo) was detected in the tumour portion of aldosterone-producing adenoma, but not in the normal control adrenals, at the protein level. Neither the activities nor the amounts of other P-450s in the tumour portion of aldosterone-producing adenoma were significantly different from those in the non-tumour portion in the adenoma and the normal control adrenals. The aldosterone content was significantly elevated, while the androstenedione content was significantly decreased in the tumour portion of the adenoma compared with that in the normal control adrenals. In Cushing's syndrome, both the activities and amounts of P-45017α and P-450c21 were significantly elevated in the tumour portion compared with the non-tumour portion of the adenoma and the normal control adrenals, while those of P-450scc and P-45011β in the tumour portion were not significantly different from the normal control adrenals. The cortisol content was significantly elevated, while the amounts of aldosterone and 18-hydroxydeoxycorticosterone in the tumour portion of the adenoma were significantly decreased compared with those in the normal control adrenals. These results demonstrate that overexpression of P-450aldo in aldosterone-producing adenoma, and those of P-45017α and P-450c21 in cortisol-producing adenoma may play some role in the pathogenesis of primary aldosteronism and Cushing's syndrome, respectively.