Bronchoscopy was performed on 101 immunocompromised patients with fever and pulmonary infiltrates. Underlying diseases were mainly hematological malignancies. In 71% of cases, etiology of pneumonia was clarified by nonbioptic bronchoscopic methods (bronchoalveolar lavage, bronchial secretions, protected specimen brush). In 51% of cases, empirical antibiotic treatment was modified following bronchoscopy. In patients with early bronchoscopy a better prognosis regarding healing and survival was observed than in those cases, where bronchoscopy was performed later during pneumonia. Bronchoalveolar lavage was particularly suited for diagnosis of Pneumocystis carinii and pneumonia due to viruses or Legionella. Sensitivity and specificity of bronchoscopy were lower for diagnosis of mycotic pneumonia and of Gram-negative or Gram-positive bacteria.