Of 13 chronic hemodialysis end-stage renal disease (ESRD) patients undergoing open-heart surgery, 7 received intraoperative hemodialysis (IHD) during cardiopulmonary bypass and 6 received hemodialysis on a routine basis (RHD). Within the groups, IHD patients had significantly lower post-operative mean serum potassium and mean plasma creatinine concentrations compared to mean preoperative values. Postoperative mean BUN tended to decrease and mean serum bicarbonate concentration was unchanged as compared to mean preoperative values. In the RHD group, however, post-operative mean serum potassium concentration tended to increase, mean serum bicarbonate concentration significantly declined and mean BUN was unchanged as compared to mean preoperative values. An average of 2.1 +/- 0.5 liters of fluid was removed from the IHD patients during cardiopulmonary bypass. Post-operatively, 0 of 7 IHD patients versus 4 of 6 RHD patients required parenteral sodium bicarbonate therapy (chi 2, p less than 0.01). On average, RHD patients required hemodialysis 1 day after surgery, whereas IHD patients were hemodialyzed 2 days after surgery (p = 0.009). We conclude that IHD lessened postoperative hyperkalemia and metabolic acidosis and delayed postoperative hemodialysis by an additional day. IHD should be considered as an adjunct to RHD therapy in the management of ESRD patients undergoing open-heart surgery.