We assessed 10 patients with human immunodeficiency virus (HIV) infection (nine of whom had AIDS) and solitary pulmonary nodules (SPNs) that were detected on roentgenograms. Five of the patients presented with respiratory symptoms. The etiology of the SPN was determined for eight of these patients: six had infections (hydatidosis, mucormycosis, or infection with Nocardia asteroides, Cryptococcus neoformans, cytomegalovirus, or Pneumocystis carinii), one had non-Hodgkin's lymphoma, and the remaining patient had round atelectasis. Sputum studies were of no diagnostic value in any of these cases. Fiberoptic bronchoscopy with bronchoalveolar lavage and transbronchial biopsy was diagnostic in two of seven cases, and percutaneous transthoracic needle biopsy (PTNB) was diagnostic in one of four cases. Several microorganisms that were not the cause of the SPNs were observed in samples of sputum, bronchoscopic specimens, and PTNB specimens. Thoracotomy was diagnostic in the three cases in which it was performed. We conclude that the management of SPNs in HIV-infected patients is complicated by the low sensitivity and specificity of the diagnostic tests used.