Charge propagation through a redox polymer film (poly[(vinylpyridine)Os(bpy),Cl2+/3(+)]/polyamine) containing the enzymes glucose oxidase and cellobiose oxidase was studied using potential-step chronocoulometry and cyclic voltammetry. The results were correlated with substrate response measurements made using the electrodes as amperometric biosensors. To explore the effect of enzyme loading, a series of electrodes were made with varying polymer-to-enzyme ratios but constant film thickness. The apparent charge-transport diffusion coefficient D-E drastically decreased with decreasing amount of polymer, i.e. increasing amounts of enzymes. Thus it is evident that values of D-E from pure redox polymers cannot be used to describe charge propagation in enzyme electrodes. The pH dependence of charge propagation is more pronounced for electrodes with the pure polymer than for electrodes with a mixture of enzymes and polymer. For all electrodes D-E increased with decreasing pH below pH 5. A change of supporting electrolyte, giving a marked effect on the enzyme electrode response, does not alter charge propagation through the film. This shows that the effect is derived from the enzyme action only.