The serum protein were investigated by cellulose acetate electrophoresis in normal BALB/C mice, Rauscher leukemic mice, mice which were either protected or not protected with virus vaccine against virus challenge and mice which were given vaccine only. In leukemic mouse serum γ-globulin level increased slightly as the mice approached an initial stage of leukemia. In the advanced stage of leukemia there were a decrease of γ-globulin, α-globulin and albumin and an increase of β-globulin. Twenty days after virus inoculation, an abnormal fraction, not found in normal mice, was detected between α(2)-globulin and β-globulin fractions and markedly increased according to the progression of leukemia. The abnormal fraction was considered to be specific in Rauscher leukemia.
Electrophoretic studies in mice which were protected against leukemia with vaccine revealed no such abnormal fraction but showed a marked increase of γ-globulin and β-globulin, probably due to a reaction of the host toward Rauscher leukemia. In mice which developed leukemia in spite of vaccination, the results of serum electrophoresis were the same as in the case of non-vaccinated leukemic mice. The change of serum fractions in mice which were treated with vaccine only showed an increase of γ-globulin and β-globulin.