Recently, much evidence has indicated that sex hormone-binding globulin (SHBG) and corticosteroid-binding globulin (CBG) play a role in the intracellular action of sex steroids in target cells. In the present work, expression of SHBG mRNA and CBG mRNA was demonstrated in tissues of human normal endometrium and pelvic endometriosis, using the reverse transcription-polymerase chain reaction (RT-PCR). SHBG mRNA levels were higher in pelvic endometriosis than in normal endometrium (P < 0.02), while CBG mRNA levels were lower than in normal endometrium (P < 0.05). The SHBG mRNA/CBG mRNA ratio was significantly higher in pelvic endometriosis than in normal endometrium (P < 0.01). These findings suggest that overexpression of intercellular SHBG in endometriotic tissues results in the formation of the estrogen-predominant milieu, since SHBG-bound estrogen is considered to be protected from the metabolism in liver and available in endometrial cells, thereby assisting the development of the pelvic endometriosis.