Summary:Cytokines participate in the induction and effector phases of all immune and inflammatory responses. They are therefore obvious candidates for exploitation as drugs or drug targets to promote, limit, or alter these responses in infection, allergy, autoimmunity, and other disease states. Although some cytokines and related molecules are already in clinical use, the full therapeutic potential of this class of hormones has yet to be realized, and this will depend in part on understanding their normal functions and regulation in health and disease. An overview is given of the cytokines and their receptors, their genetic and structural relationships, and the regulation of their activities by naturally occurring antagonists and other physiologic mechanisms. Some of the ways in which new therapeutic strategies are being developed from knowledge of the structure, function, and regulation of these various components of the cytokine network are outlined.