30 patients infected with HIV (20 men, 10 women; mean age 34 [26-54] years), suspected of having Pneumocystis carinii (Pc) pneumonia, had undergone bronchoalveolar lavage which proved negative for Pc. They were then kept under observation for 5 months. No transbronchial biopsy was performed. 27 patients were in stage IV of the HIV infection, and 14 had been on pentamidine prophylaxis. The most frequent diagnosis with the bronchial lavage was bacterial infection (19 patients), next most frequent was mycobacterial infection (6, atypical in 5). A neoplasia (Kaposi sarcoma; non-Hodgkin lymphoma) was found in two, with pulmonary involvement. The diagnosis remained unclear in only three patients who were treated as for Pc pneumonia. The remaining 27 patients did not receive any treatment against Pc. Nonetheless, there were no cases of Pc pneumonia in the 5 months of observation so that bronchoalveolar lavage has a negative predictive value of 90% (27 of 30), high enough to make additional bronchial biopsy unnecessary.