In a prospective, controlled study undertaken to assess renal function following infusion of radiologic contrast material, serum creatinine level was determined before scan and for three days after scan in 193 patients undergoing computed tomographic (CT) brain scan with contrast enhancement (contrast medium volume, 60 to 350 mL) and in 233 controls undergoing CT scan without infusion. Renal failure developed in four patients who had infusion of contrast material and in three patients who had no infusion (greater than or equal to 50% increase in serum creatinine level and above normal). In the high-risk group (serum creatinine level greater than or equal to 1.5 mg/dL or diabetes mellitus), renal failure developed in none of the 19 patients infused and in two of 46 in the noninfused group. It was concluded that previous uncontrolled studies may have overestimated the risk of renal failure induced by contrast material.