The origin of the signal seen in response to glucose in a polyaniline/glucose oxidase system is explored by immittance spectroscopy, by comparing data from an equivalent circuit model and the parameters obtained from a solution of the faradaic branch of the frequency dispersion for a coupled chemical-electrochemical reaction mechanism. It was shown that an RC subcircuit in the equivalent circuit model was sensitive to peroxide concentration, and the interaction of peroxide with polyaniline at potentials where it either oxidised or reduced the polyaniline was discussed. This information was used to compare the data obtained in a bulk and entrapped glucose oxidase/glucose system, and it was seen that the origin of the response could not be fully attributed to peroxide interaction in the latter case. Under anaerobic conditions with entrapped enzyme, it was proposed that a complex between the gluconolactone product of the enzyme reaction and the polymer leads to a more conducting polymer, with inherent charge compensation, and this results in the observed enhanced current signal.