Interleukin-1 (IL-1) has a number of fundamental immunoregulatory, hematologic, metabolic, and physiologic effects and thus is instrumental in the coordination of tissue interactions, such as wound healing, inflammation, and host tumor response. IL-1 stimulates the activation and differentiation of pre-B cells and T cells, chemotaxis of neutrophils, recruitment of bone marrow stem cells, stimulation of arachidonic acid metabolism, degradation of proteoglycans, and increase in basal body temperature. Altered production of IL-1 or IL-1 regulatory factors may have profound clinical consequences, such as seen in AIDS, other viral and malignant diseases, and in uncontrolled inflammatory processes. A variety of positive and negative feedback mechanisms for regulation of IL-1 production have been found; therapeutic interventions are aimed at these regulatory pathways. Through approaches interfering with the signal transduction or processing of IL-1, especially by interleukin-1-receptor antagonists (IL-1RA), future treatment modalities are on the horizon.