Human choriogonadotropin, a hormone derived from the syncytiotrophoblast cells of the placenta, is a member of the glycoprotein hormone family which also contains the pituitary hormones lutropin, follitropin and thyrotropin. These four hormones are comprised of two dissimilar subunits, one (a) being common to all four and the other (J) conferring hormonal specificity. Information is rapidly accumulating on rhe nature and regulation of the genes for these subunits, as well as the structural aspects, mechanism-of-action and physiological roles of these complex hormones. This mini review considers some of the recent advances in our understanding of human choriogonadotropin.