Since April 1973 we have treated nine patients with extracorporeal membrane oxygenation (ECMO), utilizing the spiral coil membrane lung. One patient is a long-term survivor. All patients except one showed substantial improvement in peripheral arterial oxygen tension. Four adults and two neonates were treated for critical hypoxia. Two patients were treated for cardiac failure but failed to show improved myocardial function. Complications involving perfusion circuitry, cannulation, chronic systemic heparinization, thrombocytopenia, and renal failure have been managed with minimal difficulty. However, irreversible pulmonary, neurologic, hepatic, or gastrointestinal damage due to hypoxia present before the institution of ECMO was associated with lethal complications. The ECMO has supplied adequate oxygenation to this group of nine critically hypoxic patients. Institution of ECMO at an earlier date in patients with critical hypoxia would provide a higher likelihood of survival.