This study describes the application of the modified Gran I and II methods for determination of equivalence volume in redox titrations and for calibration, i.e. for determination of the correct slope of the redox indicator electrodes, which appears to be a major problem in using these electrodes. The four new versions of the Gran II method, denoted as MG(II)B, MG(II)C, MG(II)D and MG(II)E methods, in which the problem of calibration and determination of equivalence volume are considered simultaneously are suggested and compared with MG(I)S and MG(II)A methods known hitherto. All the methods are experimentally tested and discussed.