Diabetic patients are at increased risk of wound infection after major surgery, but the effect of perioperative glucose control on postoperative wound infection rates after surgery is uncertain. We tested the effect of an insulin infusion on perioperative neutrophil function in diabetic patients scheduled for coronary artery bypass surgery. Participants (n= 26) were randomly allocated to receive either aggressive insulin therapy (AIT) or standard insulin therapy (SIT) during surgery. Blood was drawn for neutrophil testing before surgery, 1 h after the completion of cardiopulmonary bypass, and on the first postoperative day. Neutrophil phagocytic activity decreased to 75% of baseline activity in the AIT group and to 47% of baseline activity in the SIT group (P< 0.05 between groups). No important differences in neutrophil antibody-dependent cell cytotoxicity were found. This study documents a potentially beneficial effect of continuous insulin therapy in diabetic patients who require major surgery. Implications: A continuous insulin infusion and glucose control during surgery improves white cell function in diabetic patients and may increase resistance to infection after surgery.