During the period from June 1969 to Dec. 1970, the serum protein electrophoretic patterns of 44 cases ofvarious cancer patients have been studied to determine the alterations in serum protein fractions in patients whowere responding to irradiation or those failing. The serum electrophoretic pattern could be observed as anindicator of prognosis or radiosensitivity. A blood sample was obtained prior to any treatment and the follow upsampling was performed 2 times during radiation therapy. Serum total protein was determind by the method ofWolfson and serum electrophoresis was carried out by using Spinco Model RB electrophoresis system. The resultswere following; Seven cases out of cases of cervical cancer responding favorably to radiotherapy showed decreasedin Alpha-2 globuline fraction were increased. A case whose third time serum electrophoretic pattern showedmultiple myeloma type died 5 months after radiotherapy with bone metastasis. Four cases out of 9 cases offavorably responded breast cancer patients showed decreased in Alpha-2 globulin foraction compared with 2 cases ofunfavorable response showed increased in Alph-2 globulin fraction.