Necrotizing enteric lesions (necrotizing enteropathy) were encountered in 63 of 280 leukemia patients and in 6 of 128 lymphoma patients autopsied within a 5-year period. Four pathogenic mechanisms were implicated: (1) shock, (2) therapeutic necrosis of tumor or leukemic infiltrates of intestinal mucosa, (3) hemorrhage with necrosis of gastrointestinal mucosa, and (4) traumatic mucosal erosions. Combinations of these 4 were frequent. Invasion of enteric bacteria through the mucosal breaks with ensuing bacteremia and bacterial shock was not unusual. Chemotherapy and adrenal corticoids, individually or in combination, were probably responsible for some of the initial lesions, inhibition of host resistance, and promotion of bacterial dissemination. Twelve patients had surgical complications.