A total of 136 patients with mild to severe uncomplicated essential hypertension were evaluated in a multicenter, randomized, double-blind, double-placebo, parallel study to compare the effect of lisinopril, a new angiotensin-converting enzyme inhibitor, with that of nifedipine. Following a 2-week placebo control period the patients were treated with either 20-80 mg/day of lisinopril (n = 89) or with 40-80 mg/day of nifedipine (n = 47). Blood pressure was significantly reduced in both groups after 4, 8, and 12 weeks of treatment. There was no difference in the effect of lisinopril compared to nifedipine. No serious clinical or laboratory adverse experiences were observed during the study. The incidence of clinical side effects was significantly lower in the lisinopril group than in the nifedipine group (21.3 vs. 48.9%, p less than or equal to 0.01). There were no significant changes in laboratory data in either group. The results indicate that lisinopril is as effective as nifedipine in the treatment of uncomplicated essential hypertension and that lisinopril is well tolerated and has an acceptable safety profile.