Cytokines can be produced within the brain and are implicated as pathogenetic mediators of pathologies of the central nervous system (CNS). They cause various CNS effects, inducing fever, anorexia, sleepiness and activating the hypothalamus-pituitary-adrenal axis. Centrally administered cytokines cause peripheral effects such as induction of the synthesis of hepatic acute-phase proteins (APP). Some of their effects (e.g. anorexia, APP synthesis, fever) may result from both central and peripheral actions. Some represent feedback mechanisms that inhibit excess cytokine production.