Poly(aniline)-poly(styrenesulfonate) composite-coated glassy carbon electrodes are shown to produce a stable, reproducible amperometric response to NADH in citrate-phosphate buffer at pH 7. These responses have been studied as a function of electrode potential, film thickness and both NADH and NAD(+) concentration. The results show that the oxidation of NADH occurs throughout the whole of the film and that NAD(+), the reaction product, reversibly inhibits the reaction. Rate constants for the different processes have been obtained by kinetic modelling and compared with those previously determined for poly(aniline)-poly(vinylsulfonate) films. Preliminary comparisons imply that diffusion within 'pores' in these poly(aniline) composite matrices is important in determining the magnitude of the amperometric responses.