The antihypertensive and metabolic responses to delapril and captopril in hypertensive patients were studied. Forty-six hypertensive patients entered the study and were divided into two groups. The delapril group included 21 essential hypertensive and five renoparenchymal hypertensive patients; while the captopril group included 11 essential hypertensive and nine renoparenchymal hypertensive patients. The patients in the delapril group took delapril 7.5 mg twice a day for 2 weeks. If the antihypertensive effect was inadequate, the dose was increased to 15mg twice a day, and then to 30mg twice a day. The period of delapril treatment was 12 weeks. The patients in the captopril group took captopril 25 mg twice a day or three times a day for 12 weeks. After delapril treatment, there were significant decreases in the systolic (from 163 +/- 17 to 141 +/- 15 mmHg) and diastolic blood pressure (from 105 +/- 13 to 91 +/- 10 mmHg). There were also significant decreases in the systolic (from 161 +/- 18 to 141 +/- 24 mmHg) and diastolic blood pressure (from 100 +/- 10 to 90 +/- 12 mmHg) after captopril treatment (p < 0.001). The pulse rates in both groups showed no significant changes after treatment. The laboratory data in both groups showed few changes after treatment. Plasma renin activity increased after delapril treatment. A cough was the side effect most commonly seen. We conclude that hypertensive patients have the same blood pressure and metabolic responses to delapril as captopril.