Fourteen patients with normal preoperative renal function underwent aortocoronary bypass graft using cardiopulmonary bypass (CPB) with pulsatile (P;n = 7) or non pulsatile (NP;n = 7) perfusion. In the two groups prebypass values of plasma renin activity (PRA) and urine beta 2-microglobulin (beta 2-M) were within normal limits. PRA increased significantly during CPB and the first 6 h after CPB only in the non-pulsatile group. In both groups, the urine beta 2-M level increased significantly during and after CPB; however, there was no significant difference in urine beta 2-M levels between the two groups. Also, the amount of beta 2-M excreted in urines per unit of time increased significantly in both groups during and after CPB; there was no significant difference between the two groups.