Previous studies have shown that peroxide caused electrophysiological damage. The present study investigates the action of agents that interfere with a free radical process in an effort to define the mechanism of peroxide damage. Deferoxamine chelates iron, making it unavailable for the Fenton reaction and thereby preventing the formation of hydroxyl free radicals from peroxide. Dimethylsulfoxide (DMSO) scavenges hydroxyl free radicals. Trolox-C, a water soluble Vitamin E analog, is an antioxidant that can scavenge peroxy radicals. Slices of hippocampus were removed from brains of euthanized guinea pigs. Electrical stimulation of an orthodromic pathway to CA1 region evoked a synaptic response and a population spike. Input-output curves were generated to evaluate the protection by deferoxamine, Trolox-C, and DMSO on the synaptic damage and impaired spike generation caused by peroxide. Lipid peroxidation was measured by the thiobarbituric acid test. Peroxide was found to increase lipid peroxidation. Deferoxamine and Trolox-C protected against the peroxide-induced synaptic damage, impaired spike generation, and lipid peroxidation. DMSO was ineffective synaptically but reduced peroxide damage to spike generating mechanisms and further lipid peroxidation. The data support the hypothesis that peroxide causes damage through a free radical mechanism.