We report 50 immunocompromised patients with pulmonary infiltrates who underwent fibreoptic bronchoscopy, including bronchoalveolar lavage, on 56 occasions. The underlying diseases were mostly lymphoma, leukemia, other malignancies and renal failure. The commonest immunodeficiency factors were chemotherapy, steroids and neutropenia. A positive diagnosis could be made from analysis of the bronchoalveolar lavage on 59% (33/56) occasions. This was a comparable yield to transbronchial lung biopsy 57% (16/27), and superior to proximal airways wash 24% (13/55), or bronchial brushings 29% (10/34). Open lung biopsy added additional diagnostic information in three of the four cases in which it was performed. The most common final diagnoses were bacterial, viral or Pneumocystis carinii pneumonia and recurrent malignancy. We conclude that bronchoalveolar lavage is a safe procedure with a high diagnostic yield in the immunocompromised host with suspected opportunistic pneumonia.