Changes in arterial blood gases as a result of transporting 28 stable postoperative cardiovascular surgical patients to the intensive care unit were studied. Three methods of ventilation during the 3-minute transport period were compared. All patients were ventilated with 100% oxygen prior to transport. Nine patients were ventilated with air by a self-inflating, non-rebreathing bag. Ten patients were not ventilated at all. Nine patients were ventilated with oxygen in a closed rebreathing circuit constructed from disposable portions of the anesthesia circuit. Oxygen tension on arrival in the intensive care unit was highest in the group ventilated with the closed rebreathing circuit and lowest in the group ventilated with room air. Carbon dixoide tension rose 6.2 mm Hg/min in unventilated patients, 3.2 mm Hg/min in patients ventilated with the closed rebreathing circuit, and did not change in the group ventilated with air.