Human saliva was incubated with human enamel powder, and the lactoperoxidase activity of the saliva was measured before and after incubation. Liquidphase lactoperoxidase activity was reduced in direct proportion to the weight of enamel powder added. Lactoperoxidase molecules were adsorbed to the enamel surface in an enzymatically active conformation, and this enamel-bound lactoperoxidase activity was also measured. The adsorption of lactoperoxidase was irreversible and produced at least a 40% increase in the concentration of lactoperoxidase in the enamel surface phase as compared with its concentration in the liquid phase. Enamel-bound lactoperoxidase, as well as the free enzyme, was capable of inactivating the key glycolytic enzyme hexokinase. The implications of the adsorption phenomenon for bacterial colonization are discussed.