In the study of the changes in hemoglobin of Rauscher leukemia an OxyHb type of absorption curve was observed in the absorption curve of hemolysate, the existence of two or more components was suggested, and compared with the normal mouse, the 2nd component was observed to increase with the advance of leukemia in starch-gel electrophoresis of hemolysate, while the 1st and 3rd components were observed to decrease. In spleen hemolysate, too, the 2nd component was observed to increase. Betke-positive erythrocytes were observed to increase in number after virus inoculation and amount to 271 to 1,000 mature erythrocytes at an advanced stage. From the above-mentioned observations the conclusion was arrived at that the fetus change in a form of dis-differentiation of tumor cells caused by Rauscher virus and Thalassemia-like condition caused by the derepression of regulator genes and repressors would appear.