The use of biologically active dopants in conductive polymers allows the polymers to be tailored for specific application. The incorporation of nerve growth factor (NGF) as a co-dopant in the electrochemical properties of the NGF-modified conducting polymers are studied by impedance spectroscopy and cyclic voltammetry. Impedance measurements at the neurobiologically important frequency of 1 kHz reveal that the minimum impedance of the NGF-modified polypyrrole (PPy) film, 15 k Omega, is lower than the minimum impedance of peptide-modified PPy film (360 k Omega).Similar results are found with NGF-modified poly(3,4-ethylene dioxythiophene) (PEDOT). The microstructure of the conductive polymerfilms is characterized by optical microscopy and electron microscopy and indicates that the NGF-functionalized polymer surface topology is similar to that of the unmodified polymer film. Optical and fluorescence microscopy reveal that (rat pheochromacytoma) cells adhered to the NGF-modified substrate and extended neurites on both PPy and PEDOT, indicating that the NGF in the polymer film is biologically active. Taken together these data indicate that the incorporation of NGF can modify the biological interactions of the electrode without compromising the conductive properties or the morphology of the polymeric film.