Oxidation of malondialdehyde (MDA) by H2O2 was affected by concentrations of MDA or H2O2, pH and solvent. The reaction displayed an approximate 1:1 ratio of H2O2/MDA consumption and probably produced malonaldehyde as the oxidation product in moderate conditions. Oxidation of MDA by light-excited riboflavin produced superoxide anion, and the amount of superoxide anion generated was MDA concentration-dependent.