We report five cases of hypersensitivity pneumonitis among workers cultivating Tricholoma conglobatum (shimeji). After having worked for 5 to 20 years, they began to notice symptoms of cough, sputum, and dyspnea. They were diagnosed as having a hypersensitivity pneumonitis based on clinical features, bronchoalveolar lavage and transbronchial lung biopsy. By the double immunodiffusion test, precipitating lines between shimeji spore antigen and sera were observed in all of the patients. By enzyme-linked immunosorbent assay, the antibody activities against shimeji and three species of fungi (Cladosporium sphaerospermum, Penicillium frequentans, and Scopulariopsis species) were significantly higher in the sera of the patients than in those of normal subjects who were cultivating shimeji. Although it is not clear what causes this disease, these findings may be helpful in determining the specific antigen.