Objective: To compare the efficacy, tolerability, and safety of once-daily therapy with amlodipine 5 mg/benazepril 10 mg vs amlodipine 5 mg, benazepril 10 mg, and placebo. Design: Randomised, double-blind, placebo-controlled, parallel-group, multicentre trial. Setting: Twenty-two clinical centres, including private practice groups and academic research clinics. Patients: A total of 530 patients between 21 and 80 years of age with essential hypertension were screened for the study, and 454 were randomised to treatment with amlodipine 5 mg/benazepril 10 mg, amlodipine 5 mg, benazepril 10 mg, or placebo for 8 weeks. Results: Amlodipine 5 mg/benazepril 10 mg produced greater reductions from baseline in sitting diastolic blood pressure than amlodipine 5 mg (P < 0.03), benazepril 10 mg (P < 0.001), and placebo (P < 0.001). The response rate in the amlodipine 5-mg/benazepril 10-mg treatment group (66.4%) was better than that observed in the amlodipine 5-mg (50.0% P < 0.02), benazepril 10-mg (38.3% P < 0.001), and placebo (24.4% P < 0.001) groups. There was no significant difference in heart rate among the four groups. The incidence of oedema in the amlodipine 5-mg/benazepril 10-mg (1.7%) group was somewhat less than that in the amlodipine 5-mg (4.5%) group. Conclusions: Therapy with amlodipine 5 mg/benazepril 10 mg was well tolerated and was superior to amlodipine 5 mg, benazepril 10 mg, and placebo in reducing sitting diastolic blood pressure in patients with essential hypertension.