13 unselected premature infants with idiopathic respiratory distress syndrome (IRDS) have been treated with continuous negative pressure (CNP). A chamber was applied to the infants' body, so that the head remained outside in normal atmospheric pressure. 4 infants died during the period of treatment. 6 out of 13 differently treated IRDS-infants died over the same 6 months period. In comparison 18 out of 27 infants with IRDS died the previous year, during the same period. The frequency of IRDS in both observation periods was the same, as was the therapy of acidosis and hypoxia. The infants responded to CNP with decreased respiratory frequency, lessening of "grunting" and return of a pink skin color. Pathological examination of 3 out of 4 deceased infants in the study group revealed both atelectases and some degree of interstitial emphysema and widened capillaries. No intravascular hyaline thrombi were seen. The remaining infant died with clinical signs of coagulopathy (no autopsy). Of the 9 surviving infants in the study group one developed a hydrocephalus and subsequent mild psychomotor developmental retardation. We conclude that the CNP therapy in the chamber is an asset to the treatment of early and medium-severe cases of IRDS. We believe, that early application might prevent development of severe IRDS. The method is not recommended for severe cases.