['To identify the most important epidermal growth factor (EGF) receptor ligand in the LH or hCG signal pathway in human ovary.', 'A retrospective clinical study.', 'Tertiary university hospital.', 'Ninety-eight infertile patients who underwent IVF-embryo transfer.', 'Sera and follicular fluid were collected at the time of oocyte retrieval. The levels of EGF, transforming growth factor-alpha (TGFalpha), and amphiregulin (AR) were measured in follicular fluid and sera by using ELISA.', 'The relationships between the level of AR and level of hCG, fertilization rate, and embryo quality.', 'Amphiregulin was abundantly expressed in follicular fluid after hCG stimulation. Although large differences were found between AR and both EGF and TGFalpha in follicular fluid, no significant difference was detected in the levels of the three EGF receptor ligands in sera. The level of AR was inversely correlated with the fertilization rate and hCG level, whereas little significant association was observed between the level of AR and embryo quality.'] Is amphiregulin much more abundantly expressed than transforming growth factor-alpha and epidermal growth factor in human follicular fluid obtained from patients undergoing in vitro fertilization-embryo transfer?