In four cases of pulmonary toxoplasmosis occurring in patients with acquired immunodeficiency syndrome, Toxoplasma sp. was discovered in bronchoalveolar-lavage fluid (three cases) and in lung biopsy specimen (one case) by using the following methods: direct examination of smears stained with eosine-methylene blue fast stain, indirect immunofluorescence assay, and inoculation of MRC5 fibroblast cell line in tissue culture.