The effects of vitamin C treatment (14 mg/kg/hr) on postburn lipid peroxidation were evaluated in 12 dogs. A lymph duct above the ankle was cannulated bilaterally. Hourly lymph flow rates, plasma and lymph total protein concentrations, and plasma and lymph malondialdehyde concentrations were measured before the burn injury and for 24 hours after the burn injury. Four groups were employed: nonburn without treatment, nonburn with vitamin C treatment, burn without treatment, and burn with vitamin C treatment. The nonburn groups showed no significant differences in lymph flow rates, total protein flux, or lymph malondialdehyde level. In the burn groups the postburn hourly lymph flow rate increased by 850% without treatment and by 500% with vitamin C treatment, whereas the postburn hourly total protein flux increased by fiftyfold and twentyfold, respectively. There was a significant reduction in the postburn lymph malondialdehyde level in the group treated with vitamin C as compared with the nontreatment group. We conclude that high-dose vitamin C administration diminishes early postburn lipid peroxidation and reduces microvascular leakage of fluid and protein.