BACKGROUND The suitable parameter in PF as well as in serum that may predict the activity of endometriosis is not well described. Therefore, we tried to examine the peritoneal fluid (PF) and serum concentrations of hepatocyte growth factor (HGF) in different revised American Society of Reproductive Medicine (r-ASRM) staging and morphologic appearances of endometriosis in an attempt to determine whether HGF can be clinically useful to predict the activity of pelvic endometriosis. METHODS Peritoneal fluid was collected from 137 women with endometriosis and 57 women without endometriosis during laparoscopy and blood sampling was collected from 37 women with endometriosis and 21 women without endometriosis before laparoscopy. The concentration of HGF in PF and serum was measured by enzyme-linked immunosorbent assay. The ability of isolated macrophages and stroma to secrete HGF in response to lipopolysaccharide (LPS) was evaluated. RESULTS A significantly increased concentration of HGF in PF was found in women with endometriosis (1451.75 +/- 90.7 pg/mL) than that in non-endometriosis (1120.5 +/- 77.3 pg/mL, p < 0.01) without any remarkable difference in HGF levels between women with stage I-/II endometriosis and stage III-/IV endometriosis. When we distributed serum and PF levels of HGF according to different color appearances of endometriosis, we found a significantly higher serum and PF levels of HGF in women containing dominant red peritoneal lesions in pelvic cavity (740 +/- 109.3 pg/mL for serum; 1685 +/- 183.4 pg/mL for PF) than those having other pigmented lesions (649 +/- 79.5 pg/mL, p < 0.05 for serum; 1224 +/- 67.8 pg/mL, p < 0.05 for PF) or chocolate cysts (485 +/- 43.1 pg/mL, p < 0.05 for serum; 1118 +/- 83.1 pg/mL, p < 0.01 for PF). Exogenous stimulation with LPS significantly increased the production of HGF in the culture media by macrophages and stroma derived from women with endometriosis than that in women without endometriosis. CONCLUSIONS These results suggest that women with early or advanced endometriosis as measured by r-ASRM scoring system are not associated with an increase in either serum or PF concentrations of HGF. Rather HGF levels in serum and PF were significantly increased in women harboring blood-filled red peritoneal lesions and may be clinically useful to predict the activity of pelvic endometriosis.