several viral diseases produce active infection in the brain. Glial and possibly neuronal cells synthesize IL-1 ,TNF , and IL-6 . Ciliary neurotrophic factor (CNTF) is also synthesized by neural as well as neuronal cells. These cytokines produced within the brain itself appear to play a role in the production of fever. When a cytokine is injected directly into the brain of experimental animals, the dose required to cause fever is several orders of magnitude lower compared with intravenous injection. Thus, it appears that central nervous system (CNS) production of these cytokines can raise the hypothlamic set-point, bypassing the circumventricular organs involved in the fever that results from circulating cyokines. Local production of cytokines in the CNS may account for the hyperpyrexia of CNS hemorrhage noted above.