The growth of Lactobacillus fermentum H3, L. fermentum Y6, and L. delbrueckii subsp. delbrueckii NRIC 1053(T), which do not grow well and accumulate hydrogen peroxide in the culture medium under ordinarily aerobic conditions, was gradually enhanced by increasing the concentration of peroxidase up to 100 U. In addition, the concentration of hydrogen peroxide accumulated was decreased by adding 100 U of peroxidase to the culture medium. These findings indicate that peroxidase efficiently catalyzes the decomposition of hydrogen peroxide accumulated during aerobic growth of the strains tested. A physiological role for peroxidase, for example NADH peroxidase, in the aerobic growth of lactic acid bacteria is discussed.