In Sprague-Dawley rats, retinal ischemia was induced by occlusion of the central retinal artery, while reperfusion was initiated by unclamping and removing the occluder. Ninety minutes of regional ischemia followed by 24 h of reperfusion resulted in a development of retinal edema in the inner plexiform layer and a migration of neutrophils into the retinal tissue. Oxygen free radicals have been implicated as inducers of cell damage in different tissues. This finding has led us to speculate that, if oxygen free radicals play an important role in the development of reperfusion injury, superoxide dismutase (SOD) and EGB 761 (Tanakan, extract of Ginkgo biloba, IPSEN) should be protective against reperfusion-induced injury. Under our experimental conditions, SOD dose-dependently reduced the development of edema formation (which was expressed in micrometers, measuring the thickness of the inner plexiform layer). Thus, 3,750, 7,500 and 15,000 U/kg of SOD reduced the reperfusion-induced edema formation from its drug-free ischemic value of 112 +/- 4 to 107 +/- 7, 91 +/- 6 (p less than 0.05) and 85 + 4 microns (p less than 0.001), respectively. Furthermore, SOD significantly reduced the migration of neutrophils which can also contribute to the development of reperfusion-induced injury. The same protective effect was observed, concerning the edema formation and neutrophil migration, in the EGB 761-treated groups. Our results indicate that free radicals play an important role in the development of reperfusion-induced injury, and the treatment of ischemic and reperfused retina with free radical scavengers may reduce the severity of reperfusion damage.