The antihypertensive activity and the influence of adrenal cortex hormones of benazepril versus captopril were studied in 30 essential hypertensives in a double-blind, randomised, placebo-controlled trial during eight weeks of treatment. Patients started with 50 mg of captopril or 10 mg of benazepril once daily; if normotension had not been obtained after four weeks of treatment the doses were increased to 50 mg twice daily or 20 mg once daily, respectively. 11-Oxycorticosteroids and progesterone in males were measured in blood and daily urine at baseline and at the 4th and the 15th days of drug administration, as well as aldosterone in daily urine by radioimmunoassay, and compared with these data in 15 healthy subjects. Following eight weeks of treatment in 64% and 56% of patients treated with benazepril and captopril respectively, blood pressure was normalised. In the corresponding remaining 14% and 13%, diastolic blood pressure decreased by 10 mmHg and more but not below 90 mmHg. Before treatment excretion of 11-oxycorticosteroids, progesterone and aldosterone was significantly increased without changes in blood levels. After two weeks of treatment 11-oxycorticosteroids and aldosterone excretion decreased (P < 0.05) without progesterone changes, benazepril treatment being more effective in decreasing 11-oxycorticosteroids levels in blood (P < 0.05). In patients with high pretreatment levels of 11-oxycorticosteroids in urine we have noticed the highest antihypertensive effect of both drugs. The main conclusions are that both the ACE inhibitors are effective in mild to moderate essential hypertensives and might decrease glucocorticoids in urine and blood.