Epithelial ovarian carcinomas originate in the ovarian surface epithelium (OSE). In culture, OSE undergoes epithelio-mesenchymal conversion, an event mimicking a wound response, while ovarian carcinomas retain complex epithelial characteristics. To define the onset of this increased epithelial autonomy in ovarian neoplastic progression, we examined mesenchymal conversion in OSE from 25 women with no family histories (NFH-OSE) and 13 women with family histories (FH-OSE) of breast/ovarian cancer (including 8 with mutated BRCA1 or 17q linkage) and in 8 ovarian cancer lines. After 3-6 passages in monolayer culture, most NFH-OSE exhibited reduced keratin expression and high collagen type III expression. In contrast, keratin remained high but collagen expression was lower in p. 3-6 FH-OSE. This difference was lost in SV40-transformed lines, which all resembled FH-OSE. Most carcinoma lines remained epithelial and did not undergo mesenchymal conversion. In 3-dimensional (3-D) sponge culture, NFH-OSE cells dispersed and secreted abundant extracellular matrix (ECM). FH-OSE remained epithelial and did not secrete ECM. ECM production was also reduced in SV40-transformed lines. Carcinoma lines in 3-D formed epithelial cysts, aggregates and papillae and lacked ECM. Sponge contraction (a mesenchymal characteristic) was greater in NFH-OSE than in FH-OSE both before and after SV40 transformation and was absent in the cancer lines. Our results suggest that increased autonomy of epithelial characteristics is an early indicator of ovarian neoplastic progression and that phenotypic changes indicative of such autonomy are found already in overtly normal OSE from women with histories of familial breast/ovarian cancer.