The sympathetic nervous system plays an important role in energy metabolism. This review deals with the type of adrenoceptors involved in catecholamine-induced thermogenesis. In healthy lean males, both beta 1- and beta 2-adrenoceptors are involved in sympathetically-mediated thermogenesis, whereas alpha-adrenoceptors probably do not play an important role. Although there seem to be no firm data to support the involvement of beta 3-adrenoceptors in human energy metabolism, conclusive evidence to exclude a significant role of beta 3-adrenoceptors in man is also lacking. In normal weight man, skeletal muscle is an important site of localization for sympathetically-mediated thermogenesis, but a contribution of other tissues, such as adipose tissue, cannot be excluded.