Publisher Summary This chapter discusses a few dissociations found among the parameters of activation and present models, which may be useful in understanding the meaning of lymphocyte activation. It also highlights several metabolic processes that have been reported to change following the stimulation of lymphocytes. The cyclic AMP levels change dramatically over very short periods of time, making it difficult to interpret the meaning of any given quantitative measure at a given point in time. In a study described in the chapter, the mitogenic lectins, concanavalin A, and pokeweed mitogen induced the later gradual increase in cyclic AMP-dependent protein kinase activity, whereas the nonmitogenic mushroom lectin (AbL) and wheat germ agglutinin induced no change in protein kinase activity. DNA synthesis is not a complete measure of lymphocyte activation.