The renal effects of a single oral dose of placebo v a new dihydropyridine calcium antagonist, isradipine, were investigated in 12 patients with mild-to-moderate essential hypertension. Six patients (group A) had normal creatinine concentrations greater than 1.6 mg/dL. Patients maintained a constant daily intake of approximately 120 mmol of sodium and 50 mmol of potassium. Measurements were taken at 30, 60, and 90 min after drug administration. Results indicated that isradipine at a dose of 5 mg once daily produced significant antihypertensive and renal responses. In conclusion, there is therapeutic benefit with isradipine independent of the status of renal function.