Strong evidence of fluoride substitution on the pyrrole ring during electrolysis has been observed in a systematic structural and thermal analyses of polypyrrole doped with BF4- by direct insertion probe-mass spectrometry. To get a better understanding, not only polypyrrole samples doped with different dopant levels but also dedoped polypyrrole samples, mechanical mixtures of polypyrrole and N(Bu)(4)BF4 were analyzed using pyrolysis mass and FTIR spectroscopy techniques.