Fever is one of the best examples of responses to injury and infection which depends on neuroimmune interactions. Cytokines function as mediators of fever, acting locally within damaged tissues, circulating factors and the brain. The primary endogenous pyrogens. IL-1, IL-6 and TNF-alpha act at each of these sites and interact with nervous and endocrine systems to modify host defence responses. Understanding the role and mechanisms of cytokine actions in fever is relevant to many other aspects of neuroimmunology, and host responses to pathological challenges.