Considerable attention has been focused recently on respiratory distress syndromes occurring in newborn infants, particularly in premature infants. Most of these illnesses are acute, occurring immediately or very shortly after birth and soon terminating in either death or complete recovery. Since 1956, five cases of an entirely different kind of respiratory syndrome have been seen at the Los Angeles County Hospital premature nursery. The clinical courses have all been similar, in that dyspnea and cyanosis developed gradually and cor pulmonale tended to appear. A most striking and consistent finding has been the extensive radiographic changes seen in all the infants. Exhaustive laboratory tests have failed to demonstrate specific infectious agents or systemic illnesses associated with pulmonary pathology. Clinically these cases resembled the socalled interstitial plasma-cell pneumonia, but histological examination of the lungs unequivocally differentiated the two. 3,6 Histological appearance of the lungs of two infants, however, closely resembled that seen