Sensitive acute renal clearance methodology was used to investigate the incidence of radiocontrast-induced nephrotoxicity in patients undergoing cardiac catheterization. Patients at the University of Oklahoma Teaching Hospitals scheduled for elective cardiac catheterization had their creatinine clearance measured on the day preceding and the day following their procedure. All patients had a serum creatinine concentration lower than 175 μmol/l. The creatinine clearance was calculated from the mean of four consecutive 30-minute renal clearance periods obtained in the fasted state during water loading. The change in renal function following the catheterization was evaluated. There was no significant change in the creatinine clearance after the cardiac catheterization (C(cr) 101.5 ± 6.4 ml/min before and 111.6 ± 7.4 ml/min after the procedure). A decrease in C(cr) exceeding 25% occurred in 1 of 23 subjects (4.3%). Patient age, presence of diabetes, and volume of contrast agent were not adverse risk factors. The results suggest a low risk of nephrotoxicity in low-risk patients undergoing elective cardiac catheterization, even when very sensitive measures of glomerular filtration rate are utilized.