CGB3, also known as choriogonadotropin subunit beta, is a member of the glycoprotein hormone beta chain family and encodes the beta 3 subunit of chorionic gonadotropin (CG). It stimulates the expression of GCM1 target genes, including the fusogenic protein syncytin-1, to promote placental cell fusion. It synthesized in large quantities by the developing placenta, reaching peak concentrations in maternal blood during the late first trimester and early midtrimester of pregnancy. It is expressed exclusively by trophoblasts. It is an important biomarker in pregnancy and oncology, where it is routinely detected and quantified by specific immunoassays. Recombinant human CGB3, fused to His-tag at C-terminus, was expressed in insect cell and purified by using conventional chromatography techniques.