AIM:To investigate the effects of 17β-estradiol on the expression of macrophage migration inhibi-tory factor ( MIF) in cultured endometrial stromal cells from endometriosis .METHODS:Immunohistochemistry was used to identify the endometrial stromal cells .The expression of MIF at mRNA and protein levels was assessed by RT-PCR and Western blotting .RESULTS:Elevated expression of MIF at mRNA and protein levels was observed in the cultured endom-etrial stromal cells treated with 17β-estradiol.In endometrial stromal cells from the women with endometriosis , the level of MIF up-regulation by 17β-estradiol was significantly higher than that in the cells from the women without endometriosis . CONCLUSION:Endometrial stromal cells from endometriosis are more sensitive to 17β-estradiol, which up-regulates the expression of MIF and contribute to the pathogenesis and progression of endometriosis .