Cholesterol oxidase (ChOx) has been covalently immobilized onto poly(aniline-co-pyrrole), electrochemically deposited onto indium-tin-oxide (ITO) glass plates, using glutaraldehyde as a crosslinker. These poly (An-co-Py)/ChOx films have been characterized using UV-visible spectroscopy fourier transform infrared spectroscopy, scanning electron microscopy, and photometric and amperometric techniques, respectively. The poly(An-co-Py)/ChOx bioelectrodes have been utilized for cholesterol estimation in the range of 1-10 mM. The ChOx activity in poly(An-co-Py)/ChOx bioelectrocle has been found to be the highest at pH 7.0 at 25 degrees C. The sensitivity and stability of poly(An-co-Py)/ChOx bioelectrode have been experimentally determined as 93.35 mu A/mM and 10 weeks at 4 degrees C, respectively. (c) 2007 Wiley Periodicals, Inc.