MANY of the severe metabolic and physiological derangements accompanying large thermal injuries have been controlled by appropriate therapy after definition and characterization of these disorders by clinical observation and laboratory investigation. Disturbances of cellular defense mechanisms, however, have been incompletely characterized, and the relationship of such changes to the subsequent development of infection has not been established. Since the introduction of the lysosomal concept by DeDuve,1 there have been numerous studies which have linked the lysosomal integrity of leukocytes with their capacity to kill ingested organisms following phagocytosis. Lysosomal function has also been linked to self-destructive processes, allergic disorders, inflammatory lesions, and shock, all of which could be of importance in burn injury.2-4 This investigation was done to study the changes in serum and leukocyte lysosomal enzymes in patients with large burn injuries, and to correlate these changes with the development of infection and "burn toxemia." Three enzymes, β-glucuronidase,