The effect of helium-neon irradiation on serum lipid peroxide concentrations in mice following 6-7% body surface area burns was investigated in a controlled study. Immediately following injury by an 8-sec 100 degrees C scalding, 25 mice were irradiated by a helium-neon laser at 0.05 J/cm2. A control group of the same size underwent identical treatment but received only sham irradiation. Serum lipid peroxide concentrations increased markedly in the control group at 0.5-4 h (P less than 0.0001, two sample t-test). In the laser treated group, the lipid peroxide concentrations remained relatively constant and were significantly depressed relative to the control group 4 h following burning (P less than 0.0001, two-sample t-test).