We prospectively evaluated the diagnostic role of bronchoalveolar lavage in the assessment of opportunistic pulmonary infections and the incidence of associated complications in 100 immunocompromised patients during a 9-month period. Bronchoalveolar lavage was useful in detecting the presence of Pneumocystis carinii, viruses, fungi, bacteria, and mycobacteria in the lower respiratory tract. P. carinii was diagnosed by bronchoalveolar lavage in 17 patients and by open-lung biopsy in 1. Other organisms detected by lavage, lung biopsy, or both included viruses (eight patients), fungi (four patients), bacteria (six patients), and mycobacteria (three patients). Of the 100 patients studied, 33 had infectious agents detected in the lung; in 6 of these patients, more than one organism was present. Bronchoalveolar lavage detected the infectious organisms in 30 of the patients, in many of whom an open-lung biopsy was likely avoided because of the lavage studies. Although no major complications of bronchoalveolar lavage were noted in this critically ill population, five patients did require short-term mechanical ventilation after bronchoscopy. When correctly used, bronchoalveolar lavage is a safe and useful procedure for the assessment of immunocompromised subjects with suspected opportunistic pulmonary infections.