Aeromonas hydrophila has only recently been recognized as an opportunistic pathogen in the immunosuppressed host. Three patients with A hydrophila sepsis were admitted to St. Jude Children's Research Hospital in relapse of acute lymphocytic leukemia. Nine isolates cultured from blood specimens from these patients were sensitive to chloramphenicol and gentamicin sulfate; A hydrophila was not found after treatment with these antibiotics. After consideration of the morphology, biochemical characteristics, and antibiograms of A hydrophila, we conclude that antibiotic therapy may greatly enhance recovery from Aeromonas septicemia.