Poly-p-phenylene was polymerized electrochemically on the surface of platinum and glassy carbon electrodes. The polymer film differs both in morphology and in effects of modification when a comparison is made between the modified platinum and modified glassy carbon surfaces. The modified electrodes are shown to decrease the overpotential for oxidation of such biologically important compounds as NADH, acetaminophen, catechol, p-aminophenol, and ascorbic acid. In addition to the decrease in overpotential, there is also an increase in the current for the oxidative process. The electrodes are stable chemically and electrochemically both in aqueous solution and in mixtures containing methanol, making them excellent candidates for sensing and/or electrocatalytic applications.