A previously healthy young man presented with breathlessness, diffuse pulmonary infiltrates on the chest x-ray film, and a high degree of peripheral blood eosinophilia. Analysis of bronchoalveolar lavage (BAL) fluid showed 64 percent eosinophils. A diagnosis of toxocariasis was eventually reached on the basis of a positive enzyme-linked immunosorbent assay (ELISA) for Toxocara canis. The routine performance of the ELISA test for Toxocara in the diagnostic approach to pulmonary infiltration with eosinophilia could reveal an undetermined, sometimes unsuspected, number of cases of adult toxocariasis with pulmonary involvement. A high degree of eosinophilia in the differential cell count of BAL fluid may eventually prove to be a useful clue in favor of such a diagnosis.