Allogeneic blood transfusions have been associated with impaired outcome in surgical patients. This effect may be mediated by leukocytes. Animal experiments have shown that at least some of the effect can be modified by removal of leukocytes from transfused blood. Therefore, we compared the effects of autologous + leukocyte-depleted against standard allogeneic red blood cell transfusion on postoperative immunosuppression in 24 men undergoing coronary artery bypass surgery. In the autologous + leukocyte-depleted red blood cell transfusion group, patients received 800 +/- 200 mL (mean +/- SD) autologous blood and 2.2 +/- 2.0 units (mean +/- SD) of leukocyte-depleted saline-adenine-glucose-mannitol (SAGM) red blood cells. In the standard red blood cell transfusion group, patients were transfused with 5.5 +/- 1.4 units (mean +/- SD) of SAGM red blood cells. Leukocyte and differential counts; percentages of lymphocyte subpopulations (CD3-, CD4-, CD8-, CD16-, CD20-, CD25-, and B5-positive lymphocytes) and monocytes (CD14); phytohemagglutinin-, concanavalin A-, and pokeweed mitogen-induced and unstimulated proliferation of separated lymphocytes; unstimulated and pokeweed mitogen-stimulated production of IgG, IgM, or IgA; and serum interleukin-6, interleukin-1 beta, and serum C-reactive protein concentrations were measured preoperatively and on postoperative Days 1, 7, and 21. Significant changes were seen in these variables, but there were no differences between the groups. Three of the 12 patients in the allogeneic leukocyte-containing red blood transfusion group became human lymphocyte antigen (HLA) alloimmunized. No infections or other complications occurred in any patients. We conclude that HLA alloimmunization was the only effect that could be modified by use of autologous blood.