After inhalation of leather-impregnation sprays in a confined space five patients developed acute and severe symptoms of alveolitis, with disorders of ventilation and diffusion as well as marked radiological changes. In one case without any treatment pulmonary fibrosis developed. In the other four immediate administrations of steroids produced complete healing. Inhalation of small amounts of leather-impregnation spray produced no changes in pulmonary function tests in volunteers. There were no similarities with forms of alveolitis produced by other noxious inhalation agents.