The effects of constant intravenous infusion of propranolol, 1 mg/kg/h, on acute renal failure produced by 1 h occlusion of the left renal artery in the rat were investigated by clearance and micropuncture techniques. Propranolol infusion resulted in a significantly smaller rise in proximal intratubular pressure than that observed following renal ischemia in the saline-infused group. When compared with saline-infused animals, this effect was accompanied by a significant improvement in inulin clearance without commensurate increase in renal blood flow or stop flow pressure and suggests attenuation of intratubular obstruction by the drug. A complex metabolic effect may be involved.