Mossbauer spectra of FeCl3-doped poly(phenylenevinylene) with composition [C8H6(FeCl4))(0.30)](n) and of I-129(2)- doped poly(2,5-thienylenevinylene) with composition [C6H4SI0.40](n) showed FeCl4- and symmetrical I-5(-), respectively, to constitute the dopant ions. The above doping processes are in these aspects equal to the doping processes in polyacetylene, while the corresponding processes in polyphenylene (FeCl3 doping) and polythiophene (I-2 doping) show a slightly different behavior.