The presence of hepatocyte growth factor (HGF) in follicular fluid (FF) relative to concentrations of sex steroid hormones and human chorionic gonadotrophin (HCG) was investigated. A total of 69 FF samples were obtained during oocyte retrieval for in-vitro fertilization (IVF) from 11 patients with no apparent endocrine disorders. The concentrations of HGF, oestradiol, progesterone, HCG and testosterone in FF samples were measured by enzyme-linked immunosorbent assay. Transcription of HGF and its receptor, c-met, was detected by reverse transcription-polymerase chain reaction (RT-PCR). Human FF samples contained approximately 90-fold higher amounts of HGF (24.2 +/- 1.2 ng/ml), compared with those of serum (0. 28 +/- 0.04 ng/ml). Concentrations of HGF in FF were positively correlated with those of progesterone (r = 0.649, P < 0.0001) and HCG (r = 0.264, P = 0.026) concentrations in FF. However, HGF concentrations were not significantly correlated with oestradiol and testosterone. HGF in FF was detected by Western blotting, as a single 90 kDa band, corresponding to a single chain form. Additionally, mRNA for both HGF and its receptor were detected in a crude granulosa cell preparation from the pre-ovulatory follicles. These findings suggest that HGF is produced locally in human ovarian follicles and may have a physiological role as an autocrine/paracrine factor.