Exposures to grain dust aerosols in agricultural work environments have been linked to a variety of respiratory diseases, including occupational asthma, chronic bronchitis, and hypersensitivity pneumonitis. Agricultural workers are exposed daily to grain dust through combining, grain handling, mixing of feeds, or grain processing operations. Soybeans, which account for 1/4 of the crop value in Iowa, have been damaged increasingly by Sclerotinia sclerotiorum or "white mold", a fungal pathogen. There has been an increase in health complaints of Iowa soybean farmers following exposure to white mold as the proportion of the soybean crop infected with the mold has increased. Yang (1997) reported a doubling in the extent of white mold infestation since 1995. This project will investigate the respiratory health effects of exposure to S. Sclerotiorum and other soybean bioaerosols through inhalation toxicology studies using established animal models.