Objectives: To evaluate the clinical utility of bronchoscopy with bronchoalveolar lavage (BAL) for diagnosing pulmonary infection in patients with underlying malignancy and to evaluate the impact of positive microbiology results on antimicrobial therapy. Design: Retrospective chart review. Setting: University-affiliated downtown teaching hospital in Toronto. Patient population: All patients who underwent bronchoscopy with BAL from November 1990 to September 1992. Results: One hundred and thirty-nine BALs were performed, of which 82 (59%) were positive for microorganisms. These 82 charts were reviewed. The main underlying diagnosis was hemotogenous malignancy (70 of 82). Primary indiction for bronchoscopy was the presence of pulmonary symptoms with or without radiographic abnormality. Common organisms identified were fungi (n=50), primarily Candida albicans and cytomegalovirus (CMV) (27), and 16 'usual' pathogens. Less common were herpes simplex virus (six), Pneumoncystis carinii pneumonia (PCP) (four), Legionella pneumoniae and Mycoplasma pneumoniae (one each). Eighty-seven per cent of patients were on broad spectrum antibiotics at the time of bronchoscopy. Although antiibiotic therapy was altered postbronchoscopy in 47 of the 82 cases, only 26 instances could be directly attributed to the results of BAL. Pathogens that commonly initiated specific therapy were CMV (16 of 27) and PCP (three of four). Diagnostic yield was highest in allogenic bone marrow transplant recipients (BMT). They comprised only 49% (40 of 82) of the cases but accounted for 85% (22 of 26) of those whose therapy was directly altered by the results of BAL. Of these 22 cases, 20 were attributed to the isolation of CMV. Conclusions: The overall raw diagnostic yield from bronchoscopy with BAL was high at 59%. Of those with positive BAL cultures, a change in antimicrobial management occurred in 32% of cases. In a patient poulation with underlying hematogenous malignancy, particularly BMT recipients, bronchoscopy with BAL is useful for a specfic diagnosis of pulmonary infection.