We compared blood pressure lowering effects between imidapril of 5 mg and alacepril of 25 mg. The subjects were 11 hypertensive Japanese patients (6 males and 5 females) aged 51-87 years with the mean±standard deviation of 73±10 years, and their blood pressure had been controlled well by anti-hypertensive agents including imidapril of 5 mg. After we changed the administration of imidapril of 5 mg once a day to that of alacepril of 25 mg once a day, without any changes of other anti-hypertensive agents, the systolic blood pressure (mean±standard deviation) in patients significantly increased from 130±7.5 mmHg to 140±11 mmHg (p<0.0005). The present study suggests that imidapril of 5 mg is stronger than alacepril of 25 mg for lowering blood pressure in patients with hypertension.