The records of 46 immunocompromised patients who presented with diffuse pulmonary infiltrates were reviewed to determine the role of open lung biopsy in their management. Fifty-two percent of these patients had underlying hematologic malignancies and 54 percent had received chemotherapy within 3 months prior to biopsy. Forty-six percent were receiving immunosuppressive doses of corticosteroids. A specific diagnosis was obtained in 30 of the 46 patients (65 percent). Fifteen of these patients had pulmonary infections. Nonspecific diagnoses were obtained in 16 of the 46 patients (45 percent). Therapy was altered in a total of 27 patients and 17 of these patients responded to treatment. Overall survival at 1 year was 41 percent. Forty-eight percent of the patients in whom therapy was changed survived 1 year, and 31 percent of the patients in whom therapy was not changed survived 1 year. No deaths were attributable to the operative procedure. The complication rate was acceptable. Open lung biopsy is an important technique in evaluating and determining therapy in immunocompromised patients who present with diffuse pulmonary infiltrates.