Cytokines are a unique class of intercellular regulatory proteins that play a crucial role in initiating, maintaining, and regulating immunologic homeostatic and inflammatory processes. Indeed, measurement of cytokine profiles in patients provides a useful indication of disease status. Due to their multiple functions, including regulatory and effector cellular function in many diseases, these molecules, their receptors, and their signal transduction pathways are promising candidates for therapeutic interference. The therapeutic administration of cytokines, modulation of cytokine action, or at times gene therapy is being used for a wide range of infectious and autoimmune diseases, in immunocompromised patients with AIDS, and in neoplasia.