Activities of the acidic and basic peroxidases from tomato fruit (Lycopersicon esculentum Mill. cv. Flora Dade) were determined at six ripening stages, from green to red-ripe fruits. Both the acidic and basic peroxidases reached a maximum during the climacteric, at the pink stage, but the relative increase in basic peroxidase activity was much more pronounced. Changes in the peroxidase, IAA oxidase, and ACC oxidase activities of the basic peroxidases paralleled the changes in ethylene production. However, in the presence of calcium, the degree of activation of peroxidase was constant throughout ripening, whereas the IAA and ACC oxidase activities of the basic peroxidases were only activated at the pink stage.