PQQ-dependent methanol dehydrogenase (EC 1.1.99.8) was immobilized onto the surface of a carbon paste electrode by the cross-linking method and the electrode was covered with a porous polycarbonate membrane. An electrocatalytic steady-state current for the oxidation of methanol was observed using this electrode in the presence of phenazine methosulphate as an electron transfer mediator and NH4Cl as an activator for enzyme activity. The electrocatalytic current at +0.2 V vs. Ag/AgCl was analyzed. The properties of the electrode were examined for the determination of ammonia. The electrode responded linearly to ammonia in the range of 3 to 60 mM. The assay took 40 to 50 s. The electrode was used repeatedly at room temperature for 15 days and retained 50% of its initial activity.