A novel multilayer film containing cobalt phthalocyanine was achieved on the surface of a quartz slide and gold electrode by alternating deposition of water-soluble cobalt phthalocyanine tetrasulphonate (CoTsPc) with a bipolar pyridine salt (PyC(6)BPC(6)Py). The modified electrode was shown to exhibit an excellent electrocatalytic response for the oxidation of hydrazine, therefore it can be applied as an amperometric sensor of hydrazine. Hydrazine was detected by flow-injection analysis at the modified electrode with high sensitivity. The method gave a linear range from 1 x 10(-3) mol l(-1) to 1 x 10(-6) mol l(-1) and a detection limit of 6 x 10(-7) mol l(-1) (signal-to-noise = 3).