We investigated whether human granulosa-luteal (GL) cells exhibited lipopolysaccharide (LPS)-binding protein, and the response of follicular aspirate cells to LPS in vitro. Follicular aspirates taken from a human in-vitro fertilization and gamete intra-fallopian-tube transfer programme were subjected to Percoll gradients in order to isolate an enriched population of GL cells. GL cells exhibited specific LPS-binding protein, detected by autoradiography of the cellular lysate on SDS-PAGE after the cells were specifically labelled with a radioiodinated, photoactivable and reducible LPS derivative. LPS binding to the cells was also detected by the appearance of immunofluorescence associated with the cellular membrane when incubated with a fluorescent conjugated LPS receptor antibody. Ninety-four per cent of the cells exhibiting immunofluorescent LPS-binding protein were also positive for the steroidogenic enzyme 3 beta-hydroxysteroid dehydrogenase, as detected by cytochemistry. In order to detect a response to LPS, the enriched population of GL cells were cultured in vitro in the presence or absence of LPS; after 16 h of culture, tumour necrosis factor-alpha (TNF) mRNA was detected by reverse transcription-polymerase chain reaction and Southern blot analysis of the amplified cDNA. The expression of TNF mRNA was enhanced when the cells were cultured in the presence of LPS, which also significantly enhanced TNF secretion into the media during the 16-h period. These results reveal that GL cells exhibit LPS-binding protein and thus increased TNF secretion occurs in response to LPS in follicular aspirate cells. The source of ovarian TNF may be leukocytes, macrophages and/or GL cells.