To investigate the transport of scalars by turbulent flows with different shear stresses, direct numerical simulations were performed of passive heat transfer in a plane channel and Couette flow. The simulations showed that streamwise vortices play a significant role in near wall heat transfer for both flows. At the centerline, Couette flow has large scale structures that transport heat across the centerline. In channel flow, lower turbulence levels at the centerline are not effective in breaking up packets of hot or cold fluid. This results in higher temperature fluctuations at the centerline and overall lower heat transfer than in Couette flow. (C) 2003 Elsevier Ltd. All rights reserved.