During the period from June 1969 to Dec. 1970, the serum protein electrophoretic patterns of 44 cases of various cancer patients have been studied to determine the alterations in serum protein fractins in patients who were reponding to irradiation or those failing. The serum electrophoretic pattern could be observed as an indicator of prognosis or radiosensitivity. A blodsample was obtained prior to any treatment and the follow up smapling was performed 2 times during radiation therapy. Serum total protein was determind by the method of Wolfson and serum eletrophoresis was carried out by using Spinco Model R B electrophoresis system. RESULTS : Seven cases out of cases of cervical cancer responding favorably to radiogherapy showed decreased in lpha-2 globulin fraction were increased. A case whose third time serum electrophoretic pattern showed multiple myeloma type died 5 months after radiotherapy with bone metastasis. Four cases out of 9 cases of favorably reponded breast cancer patients showed decreased in Alpha-2 globulin foraction compared with 2 cases of unfavorable response showed increased in Alph-2 globulin fraction.