PALMER, W. K. Introduction to the symposium: cyclic AMP regulation of fuel metabolism during exercise.Med. Sci. Sports Exerc., Vol. 20, No. 6, pp. 523–524, 1988. The actions of a number of hormones on cells are mediated through the plasma membranes that produce intracellular “second” messengers. The physiological functions of one of these messengers, cyclic AMP, have been well characterized in a variety of cell types. Since cyclic AMP mediates the action of β-adrenergic hormones, hormones thought to play a significant role during exercise, this symposium is directed toward summarizing what is known about the role of cyclic AMP in fuel metabolism during exercise.