Clinical observations of 16 patients were collected to exemplify a possible new disease entity. Each was a Puerto Rican migratory worker engaged in the handling of compost used as soil for growing mushrooms in Pennsylvania. The disease has not, as yet, been observed or identified in other persons. Immunity was not conferred by a single episode or successive episodes. The disease recurred with reexposure. Treatment was nonspecific and supportive. Removal of contact from the compost was necessary for cure. The consistent findings were respiratory signs and symptoms, characteristic roentgenographic appearance of lung fields, eosinophil count elevation, nationality of patient, and contact with the compost. The natural pattern of the disease resembles that of "farmer's lung" and "silo-filler's disease." The etiology remains undetermined.