The safety and efficacy of isradipine as well as its long-term effects on renal hemodynamics were evaluated in a study of 17 patients with mild-to-moderate essential hypertension and normal or slightly impaired renal function. After a 4-week placebo period, isradipine was administered according to a schedule of increasing dosages ranging from 1.25 to 5 mg twice daily. During treatment and at the latest follow-up (at 6 months), isradipine was found to lower blood pressure (diastolic and systolic) significantly. There were no significant side effects or changes in blood chemistry during treatment. Plasma renin activity and serum aldosterone were slightly raised whereas the glomerular filtration rate, renal plasma flow, and filtration fraction were significantly raised at the latest follow-up compared with the pretreatment levels.