A voltammetric study was performed in carboxymethylcellulose (CMC) aqueous solutions using platinum electrodes and polypyrrole-CMC composite films on platinum. The formation and growth of composite films on platinum from aqueous solutions of pyrrole and the polyelectrolyte at 800 mV was followed by ex-situ ultramicrogravimetry. The microgravimetric kinetics were found to depend on [pyrrole] x [CMC](0.6). The empirical kinetics determined from stored charge in the polymer (obtained by voltammetry) were found to depend on [pyrrole] x [CMC]. This disagreement was due to changes in both the productivity of the charge consumed during the polymerization (mg mC(-1)) and the storage efficiency (charge stored per milligram of electrogenerated polymer) in films generated under different conditions. The variations indicate changes in the polymerization mechanism, which were also detected from changes in the ratio of charge stored in the film to charge consumed to generate them in films electrogenerated from different concentrations of reactants for different polymerization times.