The effects of operative trauma on systemic immunity were studied. The relative effects of skin incision and of breaching the peritoneum were determined. In addition, the role of the antiendotoxic agent taurolidine in preventing postoperative immune suppression was assessed.Systemic immune responsiveness was measured as the delayed-type hypersensitivity (DTH) response to 2-4 dinitro l-fluorobenzene (DNFB) with an in vivo rat model. The effect of both laparotomy and taurolidine on the hepatic Kupffer cell population was determined by immunohistochemistry.This study confirmed that cellular immunity is significantly depressed after laparotomy (15.5%; range, 2.5%-24.0%) compared with unoperated controls (26.77%; range, 9.2%-38.0%). Opening the peritoneum appeared to be a critical factor in inducing this immunosuppression, in which animals undergoing a similar midline incision without opening of the peritoneum displayed minimal alteration in their DTH response (20.5%; range, 0.85%-41.5%). In addition, intraperitoneal administration of taurolidine in the perioperative period prevented this decrease in postoperative DTH response. Kupffer cell numbers were increased after intraperitoneal administration of taurolidine, compared with animals treated with intraperitoneal saline solution or unoperated controls.These findings confirm the presence of an operatively induced decrease in immune responsiveness and suggest that entering the peritoneum is an important factor in the induction of this effect. In addition, administration of taurolidine acts to prevent the impact of laparotomy on DTH response, possibly by preventing perioperative portal endotoxemia.