A cytokine-induced neutrophil chemoattractant (CINC/gro), which belongs to the interleukin (IL)-8 family, acts as a functional chemoattractant for neutrophils in rats. In the present study, we examined whether CINC/gro contributes to the ovulation process in the rat ovulation system. In rat ovaries, CINC/gro was immunohistochemically recognized in the theca layer of the antral follicle but not in the granulosa cells. To clarify the role of CINC/gro in the ovulation process, CINC/gro protein and mRNA were examined during pregnant mare serum gonadotropin (PMSG)-hCG treatment. CINC/gro protein did not increase as a result of PMSG injection. However, it increased rapidly after hCG injection and peaked at 6 h after hCG. CINC/gro mRNA was also strongly expressed after hCG injection. The increase of CINC/gro protein followed increases in IL-1β and tumor necrosis factor α (TNFα). In the whole ovarian dispersate culture, FSH, hCG, IL-1β, and TNFα stimulated the production of CINC/gro protein in a dose-dependent manner. In particular, the stimulatory effects of IL-1β and TNFα were stronger than those of gonadotropins. These results suggest that CINC/gro plays an important role in the rat ovulation process by attracting neutrophils. CINC/gro increased just prior to ovulation, and it may be regulated directly by cytokines such as IL-1β and TNFα and indirectly by gonadotropins.