Cytokines such as interleukin-1 and tumor necrosis factor are involved in the triggering of the immune response, induction of acute inflammatory events, and transition to, or persistence of, chronic inflammation. The action of proinflammatory cytokines is regulated by their receptor expression, downregulation and shedding, by specific inhibitors, and by inhibitory cytokines mainly produced by lymphocytes. This review aims to pinpoint recent findings in the assessment of the biologic activities of cytokine inhibitors and inhibitory cytokines. The suitability of these agents as therapeutic tools is discussed. © 1995 American Academy of Neurology.