Chorionic gonadotrophin (CG) concentration in the ‘near term’ chimpanzee placenta was similar to that of human term placentae and significantly (p < 0.05) higher than that found in term placentae of marmosets and rhesus monkeys. A significant linear relationship, correlation coefficient r= +0.999, was found between log mean placental weight and log mean CG concentration in placentae from marmosets, rhesus monkeys and the chimpan