Cilazapril is a structurally new angiotensin-converting enzyme inhibitor that lacks a sulfhydryl moiety. Its duration of action is consistent with a once-daily regimen. Cilazapril was studied in multiple-dose trials that included more than 4,500 hypertensive patients worldwide. Approximately 450 patients received cilazapril as monotherapy for more than one year, and another 430 patients were treated with cilazapril in combination with hydrochlorothiazide for more than six months. Cilazapril at doses of 2.5 to 5 mg once daily is clinically and statistically significantly more effective than placebo and as effective after eight weeks of therapy as hydrochlorothiazide, atenolol, propranolol sustained release, captopril, and enalapril at the doses recommended by the manufacturers. The overall incidence of adverse events observed during cilazapril therapy is comparable with that seen with placebo in double-blind studies. Cilazapril 2.5 to 5 mg once daily seems to be better tolerated than hydrochlorothiazide and atenolol. Only five adverse events were reported at an incidence of 1 percent or more in controlled trials; these were headache, dizziness, fatigue, nausea, and chest pain, which all occurred at a frequency similar to that with placebo. Overall, cilazapril is effective and well-tolerated in the treatment of patients with hypertension.