Adult rabbits were exposed to 3 and 4 atmospheres pressure to observe the effect of hyperbaric oxygen on the retina. Vasoconstriction and venous arteriolization occurred without altering electroretinographic response or histological appearance following exposure to high pressure oxygen. No change in electroretinographic response or in retinal histology resulted from three-hours exposure to 100% oxygen at 3 atmospheres absolute (ATA). Total electroretinographic extinction associated with extensive retinal folding occurred within three-hours exposure to 100% oxygen at 4 ATA.