A growing body of evidence suggests that mammalian ovulation bears similarities to local inflammatory reactions. Monocytes/macrophages, eosinophils, and neutrophils are known to infiltrate the area surrounding the dominant follicle before ovulation. Candidate local chemoattractants may include a family of small cytokines, also known as chemokines. In the present study, quantitative RT-PCR was used to initially identify and quantify the chemokines expressed in the preovulatory rat ovary. The chemokines monocyte chemotatic protein 1 (MCP-1), MCP-3, macrophage inflammatory protein 1alpha (MIP-1alpha), MIP-1beta, MIP-1gamma, regulated upon activation normal T cell expressed and secreted, eotaxin, interferon-inducible protein of 10 kDa, growth-regulated oncogene, lymphotactin, and fractalkine were all expressed in the PMSG-primed rat ovary 6 h post human CG. C10, T cell activation gene 3, exodus, exodus-2, cytokine-induced neutrophil chemoattractant-2, MIP-2, and lipopolysaccharide-induced C-X-C were not expressed in the PMSG-primed rat ovary 6 h post human CG. The cyclic variation of the ovary-positive chemokines was also evaluated throughout the course of a superovulated ovarian cycle. Significant preovulatory up-regulation relative to the untreated control state was documented for MCP-1 (18-fold), MCP-3 (12-fold), and growth-regulated oncogene (25-fold). In contrast, the preovulatory ovarian expression of eotaxin, fractalkine and regulated upon activation normal T cell expressed and secreted was not increased. These observations suggest that intraovarian chemokines may be responsible for the cyclic intraovarian residence of representatives of the white blood cell series.