We demonstrated the expression of corticosteroid-binding globulin (CBG) in human placenta using reverse transcription-polymerase chain reaction-Southern blot analysis and immunohistochemical and immunoblotting studies. In the RT-PCR-Southern blot analysis, only one predicted PCR product was detected without nonspecific products in all samples of human placenta and 3A (tPA-30-1) human placental cells. In Western blot analysis, polyclonal anti-CBG antibodies recognized a protein of approximately 55 kD in the protein extracts prepared from 3A (tPA-30-1) cells. Additionally, CBG mRNA expression was demonstrated by in situ hybridization in the syncytiotrophoblasts. Immunohistochemical studies performed on the placenta demonstrated the presence of specific immunoreactivity in the syncytiotrophoblast layer surrounding the chorionic villi. These findings suggest that CBG is synthesized in human placenta during pregnancy in addition to its synthesis in the liver.