An immunocompetent man developed malaise, fever, progressive weight loss, eosinophilia, and transient pulmonary infiltrates that responded to steroid treatment but recurred after its discontinuation. Examinations of feces, bronchoalveolar lavage fluid, and pulmonary tissue obtained during a 50-day period of hospitalization yielded negative results. When a new bronchoalveolar lavage sample and a new pulmonary biopsy specimen showed nematode larvae and adult worms, treatment with thiabendazole was started. However, therapy with this agent and then with mebendazole had no impact on the patient's downhill course, which ended in respiratory distress and death. Autopsy documented an overwhelming pulmonary infection with a metastrongylid nematode resembling a species of Angiostrongylus. Histologic study revealed features of necrotizing angiitis closely mimicking those of Wegener's granulomatosis. To our knowledge, this is the first reported instance of patent metastrongylid parasitism of the human pulmonary arteries with necrotizing angiitis caused by a reaction to the parasite and/or its metabolic products.