Clinical evaluation of delapril in Japan. Report from the Japan Study Group on Delapril. Delapril, a new angiotensin converting enzyme (ACE) inhibitor discovered in the laboratory of Takeda Chemical Industries, Ltd., is the result of drug design based on the structure-activity relationships of ACE inhibitors. Delapril is an antihypertensive agent with a relatively long duration of action and no SH moiety in its structure. Following administration, it is converted into two active metabolites. Delapril effectively lowered blood pressure in 73% of 1,008 patients with hypertension during clinical trials in Japan. Efficacy rates were 73% for essential hypertension, 85% for renal hypertension, and 80% for renovascular hypertension. Excellent hypotensive response was observed in all age groups, from young to elderly patients. Side effects during administration of delapril, based on subjective evidence, were reported in 80 out of the 1,008 cases (7.9%). The main symptoms included orthostatic dizziness (1.7%), dizziness (1.3%), and nausea (1.1%). Dry cough, which has attracted attention in recent years as a side effect of ACE inhibitors, was reported at a low incidence of 1.1%. In a double-blind, controlled study in patients with mild to moderate essential hypertension in which captopril served as a positive control, delapril showed superior hypotensive effect and greater safety. Data derived from the Japan Study Group on Delapril indicate that this ACE inhibitor has excellent hypotensive effects and a high level of safety. It is suitable as a first-line drug in both monotherapy and combined therapy. 