Peroxides are an important factor in oxidative reactions in foods because their decomposition can result in formation of highly reactive free radicals. Emulsifiers such as the Brijs, Tweens, and lecithin were found to contain 4-35 micromol of peroxides/g of surfactant. Peroxide concentrations in Tween 20 micelles increased in the presence of low iron concentrations but decreased when iron concentrations were high, suggesting that iron was capable of promoting both peroxide formation and decomposition. Oxidation of alpha-tocopherol was observed in micelles high in peroxides (Tween 20) but not in micelles where peroxide concentrations were low (Brij). Transition metals accelerated the oxidation of alpha-tocopherol in Tween 20 micelles, whereas EDTA stabilized alpha-tocopherol in the presence of added Fe(2+). These results suggest that surfactant peroxides could decrease the oxidative stability of food emulsions by acting as a source of free radicals, especially in the presence of transition metals.