Immunosuppressive agents are frequently used in transplant recipients for prevention of homograft rejection and in patients with leukemia for treatment of their primary disease. From 1973 to 1975, fifty-nine patients undergoing renal transplantation and forty-one patients with leukemia were treated at the University of California (Davis) Medical Center. Intestinal necrosis and perforation developed in four (7 per cent) of those receiving transplants and in four (10 per cent) of the patients with leukemia. One transplant receipient and all four patients with leukemia had extensive necrosis of both the small and large intestines. Two transplant recipients had isolated sigmoid perforations, and one had splenic flexure colonic perforation. All died from septicemia with septic shock. The etiology of these intestinal complication appears related to immunosuppressive agents, particularly high dosages of steroids. Despite the grave prognosis, early surgical intervention is the only method of dealing with these complications. Early diagnosis as well as properly timed and selected operations are necessary for the successful management of these patients.