OBJECTIVE: We investigated the expression of uPA and uPAR in eutopic endometrium of advanced stage endometriosis and control patients. METHODS: The 33 endometriosis patients and 32 controls were enrolled. Endometrial samples were obtained from 65 premenopausal women aged 29~44 years, undergoing laparoscopic surgery or hysterectomy for non-malignant lesions. Sufficient samples were collected from 33 patients with endometriosis stage III and IV and 32 controls without endometriosis confirmed by laparoscopic surgery. The mRNA expression of uPA and uPAR from eutopic endometrium were analyzed by RT-QC PCR. RESULTS: The mRNAs of uPA and uPAR were expressed in eutopic endometrium from endometriosis and normal controls throughout the menstrual cycle. Uterine endometrium from women with endometriosis expresses significantly (p<0.05) higher levels of u-PA mRNA than endometrium from normal women without endometriosis in the proliferative phase. There were no significant differences in expression of uPAR in eutopic endometrium between controls and endometriosis patients. CONCLUSION: These results suggest that eutopic endometrium from endometriosis patients may be more invasive and prone to peritoneal implantation because of greater u-PA mRNA expression than endometrium from women without endometriosis. Thus, increased proteolytic activity may be one etiology for the invasive properties of the endometrium resulting in the development of endometriosis.