Mobilities of charge carriers in poly(o-methylaniline) (PMA) and poly(o-methoxyaniline) (PMOA) films are electrochemically determined over a range of oxidation stages of the polymer films. In the low oxidation region, mobilities of both the polymers are comparable to that of polyaniline (PANI). In the high oxidation region, however, mobility values systematically decrease in the order of PANI > PMA > PMOA, showing that the bulky groups present at the ortho position play a more important role in the high oxidation region. The low mobilities of charge carriers in the high oxidation region explain why PMA and PMOA are less conducting than PANI. (C) 2004 Elsevier Ltd. All rights reserved.