Ovulation is an inflammation-like reaction in which leukocytes are postulated to have a central role. The abundance of leukocytes in the ovary varies with the stage of the cycle and a marked influx of neutrophils and monocytes into the interior of the follicle during ovulation has been observed. The intraovarian signals causing this preovulatory influx are not known. In the present study we have investigated the presence in the ovary of two chemotactic cytokines, GROalpha (growth-regulated oncogene alpha) and RANTES (regulated upon activation, normal T-cell expressed and secreted), which have specific chemotactic activity towards neutrophils/basophils/T-cells and monocytes/T-cells/eosinophils respectively. The concentrations of these cytokines were first measured in follicular fluid and peripheral blood from a group of patients undergoing in-vitro fertilization (IVF) procedures. GROalpha was found in approximately 10-fold higher concentrations in follicular fluid than in blood plasma from the same patients (P < 0.001). The concentrations in peripheral blood of GROalpha were similar and without significant variations in women during the time of gonadotrophin stimulation for IVF and throughout the normal menstrual cycle. There was no correlation between follicular fluid concentrations of GROalpha and follicular fluid concentrations of progesterone or oestradiol. Cultured granulosa-lutein cells secreted detectable amounts of GROalpha. The concentrations of GROalpha in the medium were markedly increased by the presence of the proinflammatory cytokine interleukin (IL)-1beta, with approximately 10-fold higher concentrations in the medium, compared with the controls (P < 0.001). GROalpha was localized by immunohistochemistry predominantly in the theca layer but also in the granulosa layer of the dominant follicle during the late follicular phase. The concentrations of RANTES in follicular fluid were only 1/50 of those in blood plasma (P< 0.001). RANTES protein was not detectable in the culture medium of granulosa-lutein cells neither during basal nor IL-1beta stimulated conditions. In conclusion, these results suggest that the chemokine GROalpha is one of the chemotactic signals which cause recruitment and activation of specific leukocytes within the ovulating follicle.