Abstract The spectroelectrochemical (visible range—VIS) and in situ electron paramagnetic resonance (EPR) measurements were carried out for electroactive polyindole films. Both EPR and absorption VIS spectra were analyzed using the Nernst equation. The number of electrons transferred per monomer unit during the redox process in the polymer ( n) as determined from both types of spectra is equal to 0.14 (VIS spectra) or 0.16 (EPR). The applicability of EPR data to determine the n value was verified by measurements for polypyrrole film. It seems that EPR spectra provide more credible values of the number of transferred electrons in redox reactions in the polymer matrix.