The influence of perioperative whole-blood transfusion and transfusion with erythrocyte suspension (SAG-M blood) on postoperative depression of cell-mediated immunity (CMI) was investigated in 67 patients who underwent elective resection for colorectal cancer. Cell-mediated immunity was assessed pre- and postoperatively by skin testing with seven common delayed-type hypersensitivity (DTH) antigens. The postoperative skin-test response decreased more in the patients who received whole blood (15 patients) than in those who received SAG-M blood (16 patients) (60% versus 42%, p less than 0.001) and in those who did not receive a blood transfusion (36 patients) (60% versus 40%, p less than 0.001). The enhanced postoperative immunosuppression in patients who received whole-blood transfusions persisted after matching according to age, sex, height, weight, hemoglobin and serum albumin levels, duration of surgery and diagnosis. Thus, perioperative transfusion with SAG-M blood does not enhance surgically induced immunosuppression as effectively as does transfusion with whole blood.