For several reasons, increasing numbers of patients with hypertension are treated with angiotensin-converting enzyme inhibitors and calcium channel blockers. In a twenty-four week, double-blind, randomized, parallel study, the antihypertensive effect of lisinopril (20 to 80 mg qd) and nifedipine (20 to 80 mg bid) were compared in 21 patients. Fourteen patients received lisinopril (mean dose 35 mg), and 7 patients received nifedipine (mean dose 54 mg). By the end of week 12, 8 patients had responded (supine diastolic pressure less than or equal to 90 mg) to lisinopril and 5 to nifedipine. At the end of the study supine systolic/diastolic blood pressure was reduced from 172/104 to 149/92 mmHg with lisinopril and from 171/102 to 158/94 mmHg with nifedipine. No significant difference between the two treatments was detected. Three patients were reported to have at least one clinical adverse experience during the active treatment period, 1 in the lisinopril group and 2 in the nifedipine group. No serious clinical adverse experiences were recorded. In conclusion, lisinopril and nifedipine are both effective in reducing blood pressure in patients with mild to severe hypertension. Lisinopril qd and nifedipine slow release bid produce similar decreases in blood pressure after twelve weeks of therapy and the safety profiles of the two drugs are similar.