The effects of 5 to 20 mg/day of manidipine, a dihydropyridine-type calcium channel blocker, on blood pressure and renal function were studied in 71 hypertensive patients with renal impairment (serum creatinine levels between 1.4 and 5 mg/dl). Thirty-two patients were followed for more than 48 weeks, and 22 patients remain on the treatment after 24 to 48 weeks. The study was interrupted in 17 patients. In 32 patients who were followed for more than 48 weeks, blood pressure was well controlled in 21 (65.6%) patients. In seven of these patients alpha beta- or beta-blockers were added to manidipine to control blood pressure. Only 1 of 32 patients whose serum creatinine level was below 3.1 mg/dl showed deterioration of renal function during the 48 weeks. Two of the 17 patients in whom the study was interrupted died of cerebral bleeding or pneumonia. Two patients discontinued the study because of complications of myocardial infarction and retinal infarction, six withdrew because of deterioration in renal function, and the other seven patients withdrew because of poor compliance. From these studies, it was concluded that manidipine is well tolerated and effective in hypertensive patients with renal impairment (serum creatinine levels < or = 3 mg/dl). If blood pressure is not well controlled in these patients, combined treatment with manidipine and alpha beta- or beta-blockers is recommended.