Oxidative damage to normal human brain tissue was induced following exposure to hydroxyl (OH.) or superoxide (O2-.) free radical species generated by CO60 irradiation in vitro. Both enzymic and cytoskeletal proteins showed substantial (dose dependent) oxidative damage following exposure to OH. or O2-., as quantified by SDS-polyacrylamide gel electrophoretic analysis. Extracts of Ginkgo biloba or Panax ginseng showed a remarkable capacity to protect brain tissue proteins from oxidative damage in vitro, even at extreme (2000 kRads) dosage levels of OH. or O2-.. We suggest, therefore, that the beneficial effect of these plant extracts in preventing brain tissue damage in vivo (e.g. following ischemia-reperfusion) may result from their action in protecting brain proteins from oxidative damage, in addition to their previously reported capacity to reduce free radical induced lipid peroxidation.