OBJECTIVE To study the expression patterns of steroid receptor coactivators (SRC) and steroid-induced stromal cell-derived factor-1 (SDF-1) in endometriosis, and to explore the roles of SRC in the steroid-induced SDF-1 expression endometriosis. METHODS From May 2010 to October 2012, 16 endometriosis cases at stages III or IV according to the revised American Society for Reproductive Medicine classification undergoing surgery in the First Affiliated Hospital to Nanjing Medical University were enrolled in this study. Their ectopic endometrium were from ovarian endometriomata which were identified pathologically with 9 cases at proliferative phase and 7 cases at secretory phase. The normal endometrium were acquired from the healthy women with normal menstrual cycle (n = 10, proliferative phase = 5, secretory phase = 5). The mRNA levels of SRC and SDF-1α during the menstrual cycle were detected by quantitative real-time polymerase chain reaction. Ectopic endometrium stromal cells were purified and cultured in medium containing 17β-estradiol (10(-8) mol/L) or 17β-estradiol (10(-8) mol/L) + progesterone (10(-6) mol/L). At 24, 48, 72 and 96 hours, the supernatants were collected to measure SDF-1α expression by ELISA. Ectopic endometrium stromal cells were transfected respectively with siRNA of SRC-1 and SRC-2 using lipofectamine. Two days after transfection, 17β-estradiol (10(-8) mol/L) or 17β-estradiol (10(-8) mol/L) + progesterone (10(-6) mol/L) were added into the media. On the third day after the steroid hormones treatment, the media were collected to quantify SDF-1α expression with ELISA. RESULTS (1) Cyclical changes: the SRC-1, SRC-2 and SDF-1α showed marked cyclic differences in normal endometrium (P < 0.05). In proliferative phase and secretory phase, the SRC-1, SRC-2 and SDF-1α were 5.6 ± 1.2, 3.8 ± 1.1, 2.7 ± 0.5 and 2.6 ± 1.0, 2.1 ± 1.0, 1.6 ± 0.5, respectively. There was no periodic variation in the expression of SRC-1, SRC-2 and SDF-1α in ectopic endometrium throughout the menstrual cycle. (2) Steroid-induced SDF-1α expression in ectopic endometrium stromal cells: the 17β-estradiol-induced SDF-1α expression was (1 803 ± 196), (2 272 ± 261) and (2 162 ± 258) ng/L at 48, 72 and 96 hours . At the same time points, the SDF-1α expression induced by 17β-estradiol and progesterone was (1 307 ± 150), (1 518 ± 301) and (1 550 ± 144) ng/L, respectively. There was significant difference between two groups (P < 0.05 ). (3) The effects of SRC silencing on steroid hormones-induced SDF-1α expression in ectopic endometrium stromal cells: the expression of 17β-estradiol-induced SDF-1α at 72 hours was significantly decreased from (2 313 ± 357) ng/L to (1 155 ± 244) ng/L after the silencing of SRC-1 (P < 0.05). After the silencing of SRC-2, the 17β-estradiol-induced SDF-1α at 72 hours was (1 958 ± 324) ng/L. There was no significant difference compared with the before the silencing (P > 0.05). The expression of SDF-1α at 72 hours induced by 17β-estradiol+progesterone was (1 534 ± 449) ng/L and (2 051 ± 380) ng/L respectively before and after the silencing of SRC-2 and showed the significant difference (P < 0.05). CONCLUSIONS During the expression of SDF-1α regulated by steroids in ectopic endometrium cells, SRC-1 is the major coactivator of 17β-estradiol and SRC-2 is the major coactivator of progesterone.