The effects of verapamil infusion alone and superimposed with captopril on arterial pressure and bilateral renal function were evaluated in 21 two-kidney, one-clip Goldblatt hypertensive rats and in 13 control rats. Verapamil significantly decreased arterial pressure of both hypertensive and control rats. Addition of captopril further reduced arterial pressure in hypertensive rats only. There were significant increases in glomerular filtration rate (GFR), urine flow and absolute and fractional excretory rates of sodium and potassium in the non-clipped kidney. In contrast, these renal indices decreased in the clipped kidney. Superimposed captopril during verapamil infusion did not significantly change function of the non-clipped kidney but further depressed function of the clipped kidney. In control rats, no significant change in GFR occurred in response to drugs. Renal excretion of water and sodium, but not potassium, increased after verapamil. However, the diuresis and natriuresis were less pronounced than those seen in the non-clipped kidney of hypertensive rats. There was a proportionate increase in osmolar clearance and free water reabsorption rate in the non-clipped kidney and the normal kidney. The linear relationship did not change after verapamil infusion. The results suggest that verapamil enhances the excretory function of the non-clipped kidney of Goldblatt hypertensive rats via increased GFR and decreased tubular reabsorption in the proximal and/or distal tubules despite its hypotensive action.