Bacterial pneumonia (BP) has recently been reported to be more frequent in human immunodeficiency virus (HIV)-infected patients than in normal hosts. This study reviews the clinical and radiologic manifestations of BP in 132 consecutive pulmonary episodes over a 15-month period. BP was defined on a clinical basis as a pulmonary infiltrate accompanied by fever and improving in a few days with conventional antibiotics (trimethoprim-sulfamethoxazole excluded). In patients undergoing bronchoscopy (97 procedures), semiquantitative cultures and cell differentials of bronchoalveolar lavage (BAL) were performed, in addition to conventional staining and cultures for opportunistic infections. BP were frequent (45%), and the usual community-acquired pathogens were found. The radiologic manifestations of BP were often unusual, however, and 47% were indistinguishable from the typical appearance of Pneumocystis carinii pneumonia. BAL cultures had a sensitivity of 83 or 23%, depending on whether antibiotics were administered before bronchoscopy, using a cutoff value of greater than or equal to 10(4) bacteria/ml. The specificity of BAL culture was of 80.5% if patients with P. carinii pneumonia were taken as a control group. We conclude that BP is frequently encountered in HIV-infected patients. The clinical and radiologic presentation of BP may be indistinguishable from that of opportunistic infections. Semiquantitative cultures of BAL appear a valuable diagnostic tool to avoid unnecessary invasive diagnostic procedures or treatments.