The effects of mechanical and chemical damage and three types of biotic damage on the activities of four foliar proteins of the tomato plant (Lycopersicon esculentum Mill var. Castlemart) were assayed. Proteinase inhibitor, polyphenol oxidase, peroxidase, and lipoxygenase activities were assayed in damaged leaflets and compared with activities in undamaged leaflets. These proteins are putative plant defenses in tomato. Differential induction of these proteins by the various damage-treatments was demonstrated, such that different subsets of the four proteins were induced by different types of damage. This study clearly demonstrates the ability of plants to respond differentially to different types of damage. Possible mechanisms for this differential induction and the implications of differential induction for plant defense are discussed.