Maternal serum concentrations of placental proteins 5 (PP5) and 10 (PP10) were measured by radioimmunoassay in 568 samples obtained from 308 healthy pregnant women and 63 women having toxemia of pregnancy. Below-normal PP5 values were more widely distributed in the mild than in the severe toxemia group, while the incidence of above-normal PP5 values was found only in the severe toxemia group. The incidence of below-normal PP10 values was higher in the severe than in the mild toxemia group. Our study thus suggests that simultaneous measurement of PP5 and PP10 concentrations in maternal serum in toxemia of pregnancy is a useful monitoring technique for predicting progressive pathological change and placental dysfunction related to IUGR.