Interleukin 8 (IL-8) is a chemotactic cytokine involved in the recruitment and activation of neutrophils as well as in cell proliferation and angiogenesis. Because these events are essential components of folliculogenesis, ovulation, and subsequent repair of the ruptured follicle, the presence and regulation of IL-8 in the human follicle of the menstrual cycle was investigated. The concentrations of IL-8 were higher in follicular fluids from dominant follicles of late follicular/ovulatory phase compared with those of midfollicular phase. IL-8 was detected in the media from cultured granulosa and theca cells, with 10-fold higher levels in the theca cell cultures. Exposure to FSH and LH increased the IL-8 secretion from granulosa cells, but no effect was seen in theca cell cultures. Estradiol and progesterone did not affect IL-8 secretion from any cell type. The cytokines IL-1alpha and IL-1beta, but not tumor necrosis factor alpha, enhanced IL-8 secretion from both cell types. IL-8 levels in cultures of granulosa-lutein cells from hyperstimulated in vitro fertilization cycles were not affected by either gonadotropins or steroids. These data provide evidence that ovarian IL-8 is gonadotropin and cytokine induced and may be involved in the hormonally regulated stages of follicular development and ovulation.