We controlled the hemodilution and electrolyte levels during coronary artery revascularization in chronic hemodialysis patients by hemofiltration during the period of extracorporeal circulation. Subjects comprised 7 chronic hemodialysis patients (males, average age 53) undergoing coronary artery revascularization in our department from January 1988 to December 1989. All patients had been undergoing hemodialysis for chronic renal failure and in one patient, after admission, continuous ambulatory peritoneal dialysis (CAPD) was additionally performed. During surgery, the dialyzer was equipped with an extracorporeal circulation circuit and the electrolyte level and hemodilution were adjusted using transfusion (1, 270±372ml). A large infusion volume (12, 657± 3, 966ml) was maintained and removal of water was carried out by ultrafiltration. After surgery, all patients underwent hemodialysis twice or more by the 3rd day of recovery. Concentrations of electrolytes were maintained at appropriate levels throughout the day of surgery except for one case of postoperative hypokalemia, but no marked changes in hemodynamics were observed during and after surgery. Hemofiltration during extracorporeal circulation is safe and useful in coronary surgery because it is simpler and requires less time than hemodialysis.