In the period from 1958, when Rosen and coworkers first reported a condition in which the pulmonary alveoli are filled with an eosinophilic material, to the beginning of 1964, reports of 93 cases had accumulated in the world literature, including two cases included herein. The cause of this disease, which Rosen called "pulmonary alveolar proteinosis," is not known, nor is there a known means of cure. The usual patient is a white man between 30 and 50 years of age who may do any kind of work. The first symptoms may be those of pulmonary infection or pulmonary insufficiency. Patients with pulmonary alveolar proteinosis are prone to nocardiosis and infection with other fungi. Diagnosis is made by lung biopsy. Twenty of the 93 patients reported upon were alive at the time of this review, 37 were dead and 36 had been lost to follow-up.