This study was undertaken to compare and verify the antihypertensive effects of various delapril doses versus placebo on office and ambulatory blood pressure (BP). After a 2-wk placebo period, 303 patients with mild to moderate essential hypertension were randomized in a double-blind study to 8 wk of treatment with placebo, or delapril 7.5 mg twice daily, delapril 15 mg twice daily, delapril 30 mg twice daily, or delapril 30 mg once daily. BP changes versus baseline and rates of normalized office systolic blood pressure (SBP) > 140 mm Hg and diastolic blood pressure (DBP) > 90 mm Hg, as well as responder office SBP > 140 mm Hg or reduction ≥20 mm Hg and office DBP > 90 mm Hg or reduction ≥10 mm Hg, were calculated. In the intention-to-treat population (n=296), office SBP and DBP reductions were more notable with 30 mg twice daily (15.6/11.5 mm Hg) and 15 mg twice daily (14.8/12.5 mm Hg) than with other delapril regimens (30 mg once daily: 11.8/10.5 mm Hg; 7.5 mg twice daily: 12.9/10.1 mm Hg) and placebo (P< .05 for DBP; P< .01 for SBP). The same was true for frequency of responders (63.8% and 60.3%; P≤.05 vs placebo) and normalized patients (58.6% and 53.4%; P< .05 vs placebo). Analysis of ambulatory BPs confirmed the accuracy of office BPs. Drug-related adverse events occurred in 3.4% to 6.7% of patients given delapril and in 6.5% of those given placebo. The lowest effective dose of delapril, 15 mg twice daily, may be recommended as the initial dose for patients who begin treatment with this agent.