Heparin is usually employed as an anticoagulant during routine hemodialysis. In patients at high risk of bleeding, however, use of heparin significantly increases their morbidity and, presumably, mortality. Over 1 year, we performed 156 hemodialysis procedures successfully without heparin in the transplant dialysis unit. Twenty-eight patients were included in the study; 23 patients had received renal transplants and five patients were in the perioperative period for surgery not relating to transplantation (bilateral nephrectomy, cholecystectomy, fullmouth dental extraction, and parathyroidectomy). Only one of these patients had a coagulopathy. No dialysis procedure produced or aggravated bleeding. Conversely, a coagulopathy was not induced or worsened by dialysis without heparin. A significant complication, defined as complete clotting of the artificial kidney with or without clotting in the lines, occurred in eight dialyses (5.13% of the total) and resulted in an average blood loss of 150 ml. Partial clotting of the dialyzer did not interrupt the procedure and occurred nine times (5.8% of the total). These results compare favorably with previously documented complications from low-dose and regional heparin. © 1985, National Kidney Foundation, Inc.. All rights reserved.