The kinetics of relaxation i.e. the kinetics of the doping process, have been investigated in poly(thiophene) and its alkyl substituted derivatives poly(3-methyl thiophene) and poly(3-octyl thiophene), by cyclic voltammetry. The polymer films, electrochemically deposited onto platinum and titanium electrodes, relax at various rates, depending on their structure and orientation in relation to the metal surface. The relaxation process is faster in polymers with longer alkyl chains.