Ovarian cancer is the most fatal of all gynecological malignancies. Epithelial ovarian cancer (EOC) accounts for about 90% of malignant ovarian tumours and is thought to originate mostly from ovarian surface epithelium (OSE) cells. Epidemiological data suggest that hormone replacement treatment (HRT) users have a higher risk of ovarian cancer, which is related to the use of oestrogen-only HRT. In addition, EOC is oestrogen responsive. This thesis reveals the capacity for production and metabolism of oestrogen in normal OSE and malignant primary EOC cells, and describes the action of oestrogen in the development of EOC at three levels. First, the expression of the genes encoding oestrogen production and metabolism and oestrogen receptor (ER) was investigated in OSE and EOC cells at RNA and protein levels. Immunohistochemistry revealed that steroid sulphatase (STS), oestrogen sulfotransferase (EST), 17βhydroxysteroid dehydrogenase (17βHSD) 2 and 17βHSD5 proteins were present in pre-menopausal, post-menopausal and inclusion cystic OSE as well as EOC cells. Taqman qRT-PCR revealed STS, EST, 17βHSD1, 17βHSD2, 17βHSD5, ERα, ERβ and oestrone sulphate (E1S) transporters such as organic anion transporting polypeptide (OATP)-B, OATP-D and OATP-E mRNAs were expressed in pre-menopausal OSE and EOC at different levels. When basal mRNA levels were compared among untreated samples of pre-menopausal OSE and EOC, EST mRNA expression was significantly higher in the OSE compared to EOC cells (P<0.05) while OATP-B mRNA level was the opposite (P<0.05). Radiometric enzyme activity assays demonstrated different metabolism patterns of E1S and oestrone (E1) between normal and malignant cells, indicating overall activities of STS and 17βHSD1 or 17βHSD5 to be higher than the overall activities of EST and 17βHSD2 in cancer cells while enzyme activities in OSE cells were opposite to this. Second, the impact of inflammation on oestrogen production, metabolism and action was compared in OSE and EOC cells by testing the response of target genes to a panel of pro-inflammatory cytokines. The data revealed that in OSE cells, EST (P<0.01) and 17βHSD2 (P<0.001) mRNAs were decreased while ERα mRNA (P<0.001) was increased by IL-1α. In addition, EST mRNA was inhibited by IL-4 (P<0.05). In SKOV-3 (EOC cell line) cells, IL-1α stimulated STS mRNA (P<0.001)and enzyme activity (P<0.05). Moreover, IL-4 inhibited (P<0.05) while IL-8 and IL- 10 enhanced (P<0.01) ERα mRNA levels. Finally, the effect of oestrogenic components of HRT medication (equilin and equilin-sulphate) on the expression of cancer-associated genes was compared to that of 17β-oestradiol (E2) in PEO-1 (an oestrogen-responsive EOC cell line) cells. Expression of the oestrogen-responsive genes FN1 and IGFBP3 mRNA expression was similarly inhibited by E2 and equilin (P<0.05) as well as E1S and sodium equilin-sulphate (P<0.05). In conclusion, this thesis presents evidence that intracrine oestrogen formation and metabolism differs between OSE and EOC cells, such that E2 formation is inhibited in normal OSE but is promoted in EOC. Inflammatory cytokines also influence the local production of E2 by regulating genes encoding oestrogen production and metabolism and receptors. Finally, local HRT metabolites can regulate cancer-associated gene expression in EOC. Together, these data suggest a role for local oestrogen production and action in inflammation-associated development of EOC. Conversely, differential regulation of the same parameters in OSE cells from premenopausal women minimizes oestrogen formation and ‘protects’ against the promotion of EOC.