Three consecutive groups (University of Maryland Cancer Center protocols 7110, 7405, and 7802) of patients with acute nonlymphocytic leukemia who achieved a complete hematologic remission with similar antileukemic therapy were reviewed for the development of hepatitis. Ninety-four (73 percent) experienced viral hepatitis; eight had type B hepatitis and 86 had non-A/non-B hepatitis. The hepatitis was mild in all patients. Hepatitis secondary to cytomegalovirus, herpes simplex virus, Epstein-Barr virus, or Toxoplasma gondii was not observed. Antibody to type A hepatitis was common, but acute infection could not be substantiated. All cases of type B hepatitis in which the surface antigen could be serotyped were found to have the less frequently observed ayw marker, suggesting a common donor as the source of infection. The median duration of complete remission was longer (p = 0.03) for patients in Group II (protocol 7405) who contracted hepatitis (247 days) compared with patients without hepatitis (125 days). Median overall survival was also longer (p = 0.01) for these patients in whom hepatitis developed (672 days versus 372 days, respectively). No prolongation of complete remission duration or survival could be demonstrated for patients from Group I (protocol 7110) or Group III (protocol 7802) who contracted hepatitis. In patients with hepatitis, the height of transaminase serum bilirubin levels or duration of abnormal results of liver function tests did not correlate with the duration of complete remission or survival. Hepatitis, a common infection in those patients with acute nonlymphocytic leukemia who undergo induction therapy, had an inconsistent effect on the duration of complete remission interval and overall survival.