SUMMARYIn vitro viability studies (trypan blue) on 21 canine lungs indicated that about 80% of the cells remained viable after 48 hr of storage under hypothermia and hyperbaric oxygen, but that viability had declined sharply by 72 hr.Replantation of the left lung stored by this method was performed in 38 dogs. Ten of 33 animals receiving lungs stored 24 hr were chronic survivors. None of the five dogs receiving lungs stored for a longer interval survived chronically. Seven of the 10 chronic survivors exhibited considerable function of the reimplanted lung as measured by differential bronchospirometry, compliance, and airway resistance tests from 1 to 6 months after reimplantation.The resting cardiac output was not significantly reduced in the chronic survivors studied, but marked pulmonary hypertension developed when the normal right lung was occluded.Contralateral pneumonectomy was performed on six of the chronic survivors. Two lived for 2½ hr and one for 5 hr, all with substantial oxygen uptake by the replanted lung. The major cause of death may have been right heart failure secondary to the pulmonary hypertension which developed.