In seven of 30 consecutive patients with the adult respiratory distress syndrome, disseminated intravascular coagulation (DIC) developed. Increasing respiratory dysfunction characterized by decreased effective static compliance and increased hypoxemia coincided with the development of DIC. Patients in whom DIC developed were characterized by a high incidence of bleeding, gangrene of the extremities, renal dysfunction, mortality and autopsy evidence of fibrin microthrombi in the lungs, kidney and skin. In 12 of 23 patients who did not meet the criteria for DIC, the platelet count decreased by at least 50 per cent of the initial values at some time during their illness. Fibrin microthrombi were found in the lungs in the majority of the patients subjected to autopsy. These data support the concept that depostion of platelet on damaged pulmonary capillary endothelium may be more common in the adult respiratory distress syndrome than the DIC syndrome.