Air breathing was compared with oxygen breathing during decompression from an 80-20% helium-oxygen dive to a depth equivalent to 120 fsw (4.6 ATA) in a dry chamber to see which was the most efficient gas for helium elimination. Helium elimination was measured in a closed circuit system for 90 min at the 40-fsw (2.2 ATA) stop. No significant difference was found in the efficiency of helium elimination breathing either air or oxygen in the five subjects tested.