A review was conducted of 118 episodes of serratia bacteremia in cancer patients during a 16-year period. The infection occurred most commonly in patients with acute leukemia. Most patients acquired the infection in the hospital, and 61% had received antibiotic therapy during the preceding 10 days. Fever occurred in 90% of cases and shock in 18%. Thirtyeight percent of patients had concomitant pneumonia. Patients with shock, pneumonia, or hemorrhage had a substantially poorer prognosis. The response rate was 75% for patients who received appropriate antibiotics, 22% for those who received inappropriate antibiotics, and 29% for those who received no antibiotics. Patients who continued to have positive blood culture results while receiving appropriate antibiotic therapy had a poor diagnosis. Patients who received only an aminoglycoside had the poorest response rate among those who received appropriate therapy.