Fully-developed convection heat transfer for electro-osmotic flow in a circular microtube has been investigated for arbitrary wall zeta potentials under conditions of imposed wall temperature and imposed wall heat flux. The coupled differential equations governing charge potential, momentum, and energy were solved numerically. It has been determined that elevated values of wall zeta potential produce significant changes in the charge potential, electro-osmotic flow field, temperature profile, and Nusselt number relative to previous results invoking the Debye-Huckel linearization, which is valid only for low wall potentials. (c) 2005 Elsevier Ltd. All rights reserved.