A retrospective clinical study was performed to determine the clinical impact of neutropenic enterocolitis (NE) in adult patients with acute leukemia and non-Hodgkin's lymphoma treated with cytosine arabinoside (Ara-C)-containing regimens. The diagnosis of NE was restricted to conditions with clinical signs of peritonitis, ileus, or intestinal hemorrhage. Forty episodes of NE were noted during 461 Ara-C-containing courses (8.6%) in 36 of 211 patients (17%) over a 6-year period. Clinically, 18 cases of ileus, 16 cases of peritonitis, and 6 cases of intestinal hemorrhage were recognized as the most important presentation of NE. NE started about 2 weeks after the initiation of the chemotherapy and lasted for an average of 1 week. All patients had a profound neutropenia. The incidence of septicemia was higher during courses complicated by NE (p less than 0.001). All cases of NE were treated with conservative measures. The mortality was 22.5% and represented one third of all therapy-related deaths during the pancytopenic period. The incidence of NE was significantly higher in courses consisting of high-dose Ara-C for 6 consecutive days when the drug was combined with amsacrine for 3 consecutive days (p less than 0.0001).