A high mortality rate still exists for the patient with ARDS 20 years after the severe syndrome was first formally defined. Hypoxia and hypercarbia remain major clinical challenges requiring mechanical ventilation. The pulmonary vascular bed has been identified as a prime site of injury. The major working hypothesis is that cellular injury is caused by oxyradicals produced by activated neutrophils. There is no present pharmacologic therapy based on this hypothesis. Steroids have no demonstrable effect on outcome. Major advances have been made in the use of extracorporeal membrane lungs to relieve hypercarbia and hypoxia while minimizing pulmonary oxygen toxicity and barotrauma. The most promising current technique is extracorporeal CO2 removal during venovenous perfusion. Further advances must await definition of the early stages of the ARDS.