Hypersensitivity pneumonitis.

Hypersensitivity pneumonitis, a disease caused by repetitive inhalation of nonviable organic dust, is increasingly recognized as a cause of acute and chronic lung disease in both children and adults. Twenty-one of 32 children and adults who went on a hay ride in Arkansas developed this disease. These cases are reported. The clinical manifestations, pathology, differential diagnosis, treatment, and immunologic aspects of the disease are reviewed.