A membrane enzyme electrode sensitive towards ethanol was fabricated based on poly(aniline)-poly(vinylsulfonate) modified electrodes. Using the membrane electrode design and by varying the physical parameters, we established that the membrane enzyme electrode current response was consistent with a reversible enzyme kinetic model. Under conditions in which the product concentration was negligible within the enzyme layer of the enzyme electrode, the substrate-dependent current response could be described using a coupled reaction-diffusion model based on irreversible enzyme kinetics. This is the first report on the use of poly(aniline) modified electrodes as amperoraetric biosensors for the detection of ethanol. In the second part of this work, we investigated the enhancement of steady-state current towards NADH at poly(aniline)-poly(vinylsulfonate) and poly(aniline)- poly(styrenesulfonate) modified electrodes in the presence of calcium ions, using electrochemical methods, ³¹P NMR and kinetic modelling. We observed reversible binding between Ca²⁺ and poly(aniline)-poly(vinylsulfonate) from cyclic voltammetry and steadystate experiments. The enhancement of electrocatalytic current towards NADH in the presence of between 20 and 40 mM Ca²⁺ were about 12 and 27 times for thin films of poly(aniline)-poly(vinylsulfonate) and poly(aniline)-poly(styrenesulfonate), respectively. This enhancement effect of Ca²⁺ ions on the electrocatalytic oxidation of NADH at poly(aniline) modified electrodes was much greater than those observed by workers using other mediators. From kinetic modelling of the experimental data, we found that the enhancement effect of Ca²⁺ ions was due to a large change in the polymer binding affinity for NADH or partitioning of NADH into the polymer film. The binding energy gain was estimated to be about 14 kJ mof' in the presence of 25 mM Ca²⁺. This was confirmed by measurements using solid state ³¹P NMR which indicated that NADH accumulated in the polymer film only in the presence of Ca²⁺.