To examine the renal effects of ibopamine HCl we evaluated 15 patients with New York Heart Association Class II-III congestive heart failure and mild renal insufficiency (creatinine clearance [CLcr] = 45-85 ml min-1). Diuretics and vasodilators were withheld and a sodium (Na+)-restricted diet was initiated. All patients exhibited positive Na+ balance at the time of evaluation. Hourly urine volumes, urine chemistries, serum chemistries, PAH and inulin/iothalamate clearances were determined 2 h pre and 4 h post a single 200 mg oral dose of ibopamine. Effective renal plasma flow, creatinine clearance, filtration fraction, and the fractional excretion of sodium and potassium were not significantly altered postdose. A significant increase in urine output and decrease in urine osmolality were seen at all time points postdose. A significant reduction in serum potassium (2 and 3 h) and blood urea nitrogen (1, 3 and 4 h) concentrations occurred. Measurements of glomerular filtration rate by inulin or [125I]-iothalamate produced differing results in the patient groups studied. We conclude that a single dose of ibopamine does not produce significant improvements in renal function in patients with congestive heart failure, mild renal insufficiency and positive sodium balance.