A randomized, prospective study comparing heparin with citrate (ACD) as anticoagulant during red blood cell saving was performed in 10 ASA grade I-II patients undergoing primary total hip replacement. Blood samples were taken before and after surgery and at several steps during cell saving. In the heparin group, salvaged red cells showed normal values, with the exception of decreased filtrability and moderate hemolysis. More differences in red cell quality were found in the ACD group. Mean corpuscular volume was higher (110 vs 95 x 10(-12) mL), red cell distribution was increased (17% vs 13%), osmotic resistance was lower (0.54 vs 0.43 g NaCl/L at 50% hemolysis), antioxidative reserve capacity was lower (1.9 vs 4.6 U glutathione reductase per gram of hemoglobin) and there was more hemolysis (15% vs 11%). Despite the small volume of autologous blood retransfused (388 +/- 92 mL), the differences in vitro produced significantly higher free hemoglobin levels in the patients' plasma at the end of the operation (58 vs 23 mg/dL). We conclude that heparin is preferable to citrate as an anticoagulant during autotransfusion with cell washing and immediate retransfusion.