In a prospective study the efficacy of fiberoptic bronchoscopy was evaluated in the diagnosis of infections with opportunistic pathogens, Kaposi's sarcoma and nonspecific interstitial pneumonitis in 171 episodes of pneumonitis in 151 HIV-infected patients. Samples were collected by suction through the inner aspiration channel of the bronchoscope (n = 164), telescoping plugged catheter (n = 117) and transbronchial lung biopsy (n = 82). A high incidence of infections with pyogenic bacteria (12%), Legionella spp. (5 %) and Mycobacterium tuberculosis were diagnosed (9%). Bronchoalveolar lavage demonstrated a high diagnostic rate in bacterial pneumonia (significance level greater than 10(5) cfu/ml) and a low degree (10%) of contamination (less than 1% squamous epithelial cells). Bronchoalveolar lavage was more effective than the telescoping plugged catheter in yielding a significant number of colonies in patients with bacterial pneumonia previously treated with antibiotics. Nondiagnosed pneumonitis was more frequent in intravenous drug abusers than in homosexual men (p less than 0.001).