Interleukin 1 (IL 1) is an important mediator of immune and inflammatory processes. We are examining the mechanisms of production of IL 1 during immune responses. Macrophages (MPhi) release potent levels of IL 1 in response to a wide variety of immune and inflammatory stimuli. However, in the presence of anti-Ia antibodies, IL 1 is still synthesized by murine MPhi, but fails to escape from the cell. Biochemical studies suggest that Ia participates in the processing of the Il 1 precursor accompanying the release process. Hence, a new concept is developing - Ia control of processing and export of IL 1. Another new concept has recently evolved concerning IL 1 production by murine B cells. Unlike MPhi, which produce IL 1 in response to a wide variety of stimuli, B cells required contact with T cells to produce IL 1. Also unlike MPhi, which release IL 1 into the surrounding milieu, B cell IL 1 remained cell associated. These observations provide new insights into the complex bi-directional mechanisms of T-B interactions. We are embarking on studies aimed at exploiting the ability of IL 1 to enhance immune responses against tumors. IL 1 powerfully promotes weak immune responses and many tumors suceed in vivo because of an ineffective immune response. It is therefore compelling to explore applications of IL 1 as an anti-tumor agent.