The ability of gonadotropins to act on and regulate normal ovarian surface epithelial (OSE) cells and ovarian cancer cells was investigated. Bovine OSE was used as a model to study normal OSE. Results demonstrate that follicle stimulating hormone (FSH) and the luteinizing hormone (LH) like molecule, human chorionic gonadotropin (hCG), can both stimulate (3H)-thymidine incorporation into DNA in normal OSE cells. Similar results were obtained using either purified hormones or recombinant human hormones. A human ovarian cancer cell-line OCC1 was also stimulated to grow in response to FSH and hCG, but the growth of a different human ovarian cancer cell-line SKOV3 was not affected. In addition to effects on cell growth, gonadotropins also stimulated growth factor expression. Both FSH and hCG stimulated steady state levels of keratinocyte growth factor (KGF), hepatocyte growth factor (HGF), and kit ligand (KL) mRNA in OSE cells. Previously, KGF, HGF, and KL have been shown to stimulate OSE growth. Both follicle stimulating hormone receptor (FSHR) and luteinizing hormone receptor (LHR) were observed in OSE cells by Northern blot analysis. Reverse transcription polymerase chain reaction (RT-PCR) analysis was performed on fresh and cultured OSE cells. Normal OSE was found to express FSHR and LHR both in vivo and in vitro. The PCR reaction products were sequenced and found to provide a 100% homology with the bovine gonadotropin receptor sequences previously reported. FSHR and LHR transcripts were also detected in gonadotropin responsive OCC1 cells, but not in the gonadotropin insensitive SKOV3 cells. Observations support the hypothesis that gonadotropins may influence some ovarian cancers. In summary, the current study demonstrates the novel observation that both the FSHR and LHR are expressed by bovine OSE and selected ovarian cancers. Interestingly, the actions of FSH and LH to promote OSE growth may in part be mediated indirectly through an elevation in the expression of autocrine growth factors (KGF, HGF, and KL). Ovarian cancer is more common in conditions with elevated gonadotropins such as post-menopausal women. Therefore, gonadotropin actions on the OSE are postulated to be a potential factor in the onset and progression of some ovarian cancers.