This study was designed to investigate the biological significance in intracellular expression of sex hormone-binding globulin (SHBG) and corticosteroid-binding globulin (CBG) mRNA in uterine endometrium with luteal phase deficiency (designated as out-of-phase endometrium or low serum progesterone level). The levels of such mRNAs were measured by the quantitative reverse transcription-polymerase chain reaction. Under the normal serum 17 beta-estradiol and progesterone levels in the mid-luteal phase, the levels of SHBG and CBG mRNAs in the out-of-phase endometria were not significantly different from those in the normal endometria. On the other hand, SHBG and CBG mRNA levels in the endometria of low serum midluteal progesterone level were significantly (p < 0.05) reduced and raised, respectively, compared with normal levels. These findings suggest that the synthesis of endometrial steroid-binding proteins in the out-of-phase endometrium is conserved, as that in the in-phase endometrium, whereas the decreased progesterone level might up-regulate CBG expression with down-regulation of SHBG expression.