Since it has been demonstrated that corticosteroid-binding globulin (CBG) plays a role in intracellar steroidal actions in target cells, the expression of CBG mRNA as the measure of CBG expression was investigated in human endometrial cancers in order to assess the biological implications of CBG. The level of CBG mRNA was analyzed using competitive reverse transcription-polymerase chain reaction-Southern blot analysis. While the level of CBG mRNA was significantly (P < 0.01) higher in secretory phase endometrium than in early and late proliferative phase endometrium, the level of CBG mRNA tended to decrease with advanced dedifferentiation of endometrial cancers as compared to normal endometrium. These results suggest that dedifferentiation of endometrial cancers induces a reduction in intracellular CBG synthesis.