Hypersensitivity pneumonitis due to the inhalation of spores from the edible mushroom Pholiota nameko was demonstrated. A 52-year-old mushroom worker noticed cough, exertional dyspnea, and high fever several hours after work in the mushroom-cultivating room. His examination revealed bilateral basilar crepitations, fine granular shadows in both lung fields of chest x-ray film, and slight decrease in diffusion capacity. Precipitin and macrophage migration inhibition factor were found against the mushroom spore extract and not other contaminants and molds. Histologic finding by transbronchial lung biopsy showed granulomatous alveolitis. Manifest increase of lymphocytes was found in his bronchoalveolar lavage fluid. Provocative inhalation test with the extract revealed similar symptoms and signs in his workplace eight hours after inhalation. It seems to be the first case of hypersensitivity pneumonitis to the Pholiota nameko mushroom spores.