We present results from the theoretical INDO calculations of the electronic structure for stacked eumelanins' monomers. As basic indolic components of the eumelanin structure 5,6-dihydroxyindole (DHI or HQ) and its oxidized forms (SQ and IQ) were chosen. The results reveal dependency of electronic properties of such aggregates on monomers' redox states. They point out also a tendency to localize an extra charge on one of dimers' subunits that could be suggestive of an electron hopping as a model mechanism for the electron transfer in eumelanins. (C) 2003 Elsevier Science B.V. All rights reserved.