Carbon paste electrodes (CPE), modified with zirconium phosphate (ZrP) along with some redox mediators, were prepared and shown to be active in electrocatalytic oxidation of coenzyme NADH, Nile blue (NB), methylviologen (MV), and benzylviologen (BV) were added to ZrP-containing CPE, showing a shift of their redox potentials toward the positive direction, ranging from ca. 0.20 to 0.35 V, This shift was interpreted in terms of different complexation abilities of oxidized and reduced forms of mediators with the host matrix, The modified electrodes prepared showed electrocatalytic activity for electrooxidation of NADH. The i.e-dependencies for the modified electrodes were shown to follow Michaelis-Menten kinetics. For C:ZrP:NB and C:ZrP:MV electrodes, Michaelis constants of 0.870 +/- 0.012 and 0.153 +/- 0.015 mM, respectively, were obtained. The sensitivity of C:ZrP:NB and C:ZrP:MV electrodes to NADH varied from 19.2 to 60.8 and from 18.4 to 50.9 mu A/mM . cm(2), respectively, by changing the working potential from -0.2 to 0.2 V vs, SCE,