Disc-electrophoreses of the sera from 10 normal women and 73 normal pregnant women were carried out in every gestation month. Electrophoretic patterns of the sera of normal women and normal pregnant women showed 15-30 protein fractions after staining with Amidoschwarz 10 B. The rerative concentrations of the protein fractions were measured by an automatic recording densitometer. The mean values of transferrin fraction in every gestation month increased most markedly. In 7th month of pregnacy the mean value showed a distinct increase, reaching the maximum in 10th month