The prevalence of pulmonary toxoplasmosis was assessed by a prospective analysis of 144 bronchoalveolar lavage (BAL) samples using competitive polymerase chain reaction (PCR) to avoid false-negative results due to PCR techniques. Six samples were excluded because they contained amplification reaction inhibitors. None of the samples from the 37 immunocompetent patients and only 1 sample (1.7%) from the 59 immunocompromised patients without human immunodeficiency virus infection were PCR-positive. In contrast, Toxoplasma gondii DNA was found in 6 (14%) of 42 samples from patients with AIDS. All 6 patients had ⩾40 CD4 cells/µL and anti-Toxoplasma antibodies, and 5 had other sites of Toxoplasma infection. Six other AIDS patients who had received treatment for cerebral toxoplasmosis were PCR-negative. Thus, pulmonary toxoplasmosis is frequent in AIDS patients who have other sites of Toxoplasma infection and low CD4 lymphocyte counts and who are not receiving prophylaxis.