Carboxypeptidase activity was characterized during ripening and wounding of tomato (Lycopersicon esculentum) fruit. The fruit enzyme shares substrate specificity and susceptibility to the inhibitors diisopropyl fluorophosphate and phenylmethylsulfonyl fluoride with other plant carboxypeptidases. The abundance and stability of wound-induced carboxypeptidase were developmentally regulated. Oxidative stress caused by cupric ions impaired the membrane permeability in the slices from pink fruit, resulting in leakage of the carboxypeptidase into the medium and in its redistribution in the cell. The patterns of carboxypeptidase activity did not parallel the cupric ion effect on ethylene levels. Immunogold electron microscopy studies indicated that the fruit carboxypeptidase is associated with electron-dense inclusions in the vacuole.