Ovulation is a complex process involving not only gonadotropins and steroid hormones, but also many local mediators common to inflammatory reactions, such as cytokines. Of particular interest is the ovarian interleukin-1 (IL-1) system, which may be an intermediary of gonadotropins in the ovulatory process. The preovulatory follicles have a complete and highly compartmentalized intraovarian IL-1 system including ligands, receptor, and receptor antagonist. IL-1 has been considered as the inductor of several ovulation-associated events such as prostaglandin and progesterone biosynthesis, plasminogen activator production, glycosaminoglycan generation, and enhancement of vascular permeability. The principal effector of the IL-1 system is nitric oxide. This paper analyzes the sites of synthesis and action of the IL-1 system in preovulatory follicle and its vascular dynamics as well as IL-1's mechanism of action in triggering follicular rupture.