The modulatory potency of lectins on cellular activities deserves attention from a cell biological and a clinical point-of-view. In addition to serving as tools to delineate signaling processes that follow carbohydrate-dependent cell binding, plant lectins can apparently affect certain characteristics of the host immune system in vitro and in vivo with potential clinical benefit (1 ,2 ). With respect to defense mechanisms the generation of reactive oxygen compounds such as the superoxide anion radical (O ₂ ^- ) and H₂ O₂ or the release of granule enzymes are supposed to play a notable role (3 -6 ) Deliberate enhancement of these activities by lectins may increase the host’s capacity to control growth of infectious organisms or malignant cells. Therefore, rigorous testing of plants agglutinins and endogenous lectins that have been isolated from human tissues may enable one to devise a rational lectin-mediated treatment modality This chapter describes the protocols for the respective assay procedures used to determine the effects of lectins on production of reactive oxygen compounds and release of granule enzymes