In the serum of 145 women between the 34th and 42nd weeks of pregnancy, 209 radioimmunological determinations of human placental lactogen were made, using the Pharmacia, Uppsala, Sweden, HCS Phadebas Test. Following the determination of normal HPL levels in late pregnancy, the HPL values of high-risk pregnancies were investigated in relation to normal values and compared with the clinical pattern. A satisfactory relation was found between low HPL levels and fetal growth retardation. To some extent the HPL data can also be used in monitoring severe EPH-gestosis and postmaturity. Light cases of gestosis and pregnancies involving Rh-incompatibility do not affect HPL production. The clinical findings regarding HPL levels should not be overestimated in attempting to diagnose placental insufficiency.