We reviewed 410 episodes of Pseudomonas bacteremia occurring in patients with cancer during a ten-year period. Pseudomonas bacteremia was most common among patients with acute leukemia. The majority of patients acquired their infections in the hospital, and 51% had received antibiotic therapy for other presumed or proved infection during the preceding week. Shock occurred in 33%, and 32% had concomitant pneumonia. The overall cure rate was 62%; it was 67% for patients receiving appropriate antibiotics but only 14% for those receiving inappropriate antibiotics. A one- to two-day delay in the administration of appropriate antibiotic therapy reduced the cure rate from 74% to 46%. Patients who received an antipseudomonal beta-lactam antibiotic with or without an aminoglycoside had a significantly higher cure rate than patients who received only an aminoglycoside (72% and 71% vs 29%). Patients with shock, pneumonia, or persistent neutropenia had a substantially poorer prognosis.