The prevalence of posttransplantation pulmonary infection and the importance of this complication with respect to morbidity in patients undergoing lung transplantation is significant. Over a 1-year period, case histories of all patients undergoing lung transplantation at Barnes Hospital, Washington University, were reviewed to examine the importance of organisms isolated in the donor lung in the development of subsequent invasive infection in transplant recipients. Twenty-eight of 29 bronchial washings (97%) taken from donors before retrieval grew at least one organism. The most common organisms identified were Staphylococcus and Enterobacter. In 12 of these cases (43%), similar organisms were isolated from the tracheobronchial tree of the recipients, and 6 of these recipients (21%) subsequently had invasive pulmonary infections as a result of the organism originally isolated in the donor. We recommend that antibiotic coverage in transplant recipients should be initiated on the basis of Gram stain results and modified on the basis of cultures obtained from the donor lungs. Pathologic analysis of donor lung tissue taken before transplantation was available in 12 cases. Four donors had histologic evidence of established pneumonia in the donor lung, and infections then developed in the recipients. One other patient who received a lung that had widespread bone marrow emboli and subsequent infarction later had a complete anastomotic dehiscence. An additional patient had profound early donor lung dysfunction without any evidence of rejection or infection. Pathologic findings from the donor in this case demonstrated preexistent acute vasculitis with emboli. We suggest that as preservation techniques improve, the opportunities for closer scrutiny of donor lung tissue before implantation will become increasing desirable and feasible.