Delapril was administered for 12 months to 131 patients with essential hypertension to evaluate its effect on the quality of life (QOL). In a multicenter open trial, delapril (30-120 mg/day divided into two doses; mean dose, 43 +/- 23 mg/day) was administered as monotherapy for 12 months and the QOL was assessed by a questionnaire with 37 items (before administration and at months 6 and 12 of treatment). Side effects were observed in 17 patients (13.9%), of whom 15 had cough (12.3%). Due to side effects, delapril was discontinued in seven cases (five for cough and two for other side effects). The QOL was significantly improved in the categories of general symptoms, physical symptoms and well-being, work performance, sleep, emotional state, cognitive function, sexual function, life satisfaction, vigor, and selfcontrol. It is concluded that long-term monotherapy with delapril is favorable from the points of both antihypertensive effect and enhancement of the QOL in patients with essential hypertension.