This study investigated the effect of the angiotensin-converting enzyme (ACE) inhibitor cilazapril on blood pressure in patients with essential hypertension [defined as a sitting diastolic blood pressure (DBP) between 95–120 mm Hg]. The study group comprised 43 patients (24 men and 19 women; mean age, 51 ± 10 years) with uncomplicated essential hypertension. In an open single-center design, all subjects were treated with a once-daily dose of cilazapril for 6 weeks, following a 1-week washout period. The initial dose was 2.5 mg/day. In non-responders, this dose was doubled after 3 weeks of treatment. Thirty-eight patients completed the study. One was withdrawn due to symptomatic hypotension, and four others due to noncompliance. Treatment produced a useful and significant reduction in blood pressure (systolic from 155 ± 3 to 138 ± 3 mm Hg, p < 0.01; diastolic from 103 ± 1 to 90 i 2 mm Hg, p < 0.001). No significant variations in mean heart rate were recorded. Normalization of DBP, or its reduction by > 10 mm Hg, was found in 28 patients (efficacy in 74% of cases). Cough was reported by one patient. There was no significant variation in laboratory profiles during the trial. Cilazapril proved to be a well-tolerated antihypertensive drug effective on a once-daily regimen in a high percentage of patients with essential hypertension.