During the serial transplantaion of the lymphatic leukemia some cases of myelogenous leukemia were found to occur in C(58) and AKR strain mouse. Complement fixation test was performed to found any difference in antigenicity between the original and the trasformed leukemia. Results were; 1) In leukemia of C(58) strain mouse common antigenicity are found between the two leukemias. 2) Identical results were also found in AKR strain mouse. 3) It is suggested that viruses of the two leukemias are similar, although not quite identical.