Pulmonary infections, which frequently occur during the early and late period following bone marrow transplantation for hematologic malignancies, are associated with significant morbidity and mortality. In this study the incidence, the infectious causes of pneumonia and the mortality related to pneumonia in 130 allogeneic and 290 autologous bone marrow recipients are reviewed. Both the incidence and the mortality by pneumonia were far lower in autologous than in allogeneic bone marrow recipients.