Cells, particularly lymphocytes in peripheral blood or lymphatic tissues such as thymus, spleen and lymph node, are examined by measuring an electrophoretic property, such as a fraction of the number of the cells having an electrophoretic mobility within a predetermined range to the total number of the cells to be examined, with the aid of an automatic electrophoretic apparatus which is operated in a medium of the physiological conditions and by reversing the electric field, and comparing the obtained pattern of the electrophoretic property of the cells to be examined with the pattern of the electrophoretic property of normal host-cells, in order to diagnose cancer.