The events taking place intracellularly within the central nervous system when pyrogens, putative neurotransmitters or other pharmacologically active substances raise body temperature during fever are poorly understood. Recognition of cyclic AMP as an intracellular mediator of adrenaline and glucagon-induced activation of hepatic glycolysis (Sutherland and Rall 1960) may further the understanding of these central events. Cyclic AMP is at present thought to modulate metabolic activities in many tissue and cell types including those of the mammalian brain (see reviews by Weiss and Kidman 1969; Greengard and Costa 1970; Robison et al. 1971; Bloom 1975; Daly 1975 a, b; Drummond and Ma 1975; Kebabian 1977; Nathanson 1977).