The long-term hemodynamic and antihypertensive effects of isradipine were investigated in 11 patients who had normal renal function and 9 who had reduced renal function. The dose regimen was 1.25-5 mg twice daily, depending on blood pressure response. After 24 weeks of active treatment, systolic/diastolic blood pressure decreased from 172/106 to 155/94 mm Hg (p less than 0.05) in the patients with normal renal function, and from 176/105 to 169/93 mm Hg (p less than 0.01) in those with impaired renal function. Contrary to the results of short-term treatment, no changes in inulin and p-aminohippuric acid (PAH) clearances were observed in either study group. There were no significant changes in plasma renin, aldosterone, glucose, or lipids, nor were these changes in protein excretion in either group; however, sodium excretion increased significantly in both groups. On the basis of our results, we conclude that isradipine has a place in the treatment of hypertensive patients with mild renal insufficiency.