Polyindole obtained by oxidizing coupling of indole, C8NH7, was studied either in the doped or the undoped state by FTi.r., Raman and electron energy loss (EEL) spectroscopies. Interpretation of the vibrational modes was facilitated by comparison of the absorption spectra of polyindole and those of related molecules acting as standards. The change from the doped to the dedoped st-ate of polyindole is accompanied by a reordering of the II bonds of the system characterized by the disappearance of C = N bonds and the reappearance of N-H bonds. Detailed analysis of the different spectral manifestations gives evidence for a monomer coupling involving the positions 2 and 3 of the carbon atoms.