Flow and heat transfer are studied numerically in a duct of rectangular cross section with a moving wall. The temperature of the moving wall is assumed to be constant while the other three walls are insulated. This boundary condition has important applications in the design of oil-cooled friction pairs. Results are presented for wall Reynolds numbers of 0, 100, 500, and 2500; Prandtl numbers of 0.7, 10, 50, and 100; and cross-sectional aspect ratios of 0.5 and 1. It is found that flow and heat transfer are strongly affected by an interaction between the boundary layer on the moving wall and a recirculation zone set up by that wall. In particular, the Nusselt number shows an interesting maximum before fully developed conditions are established. This maximum is believed to result from the enhancing effect of the widening recirculation zone as fully developed conditions are approached. Hydrody-namic and thermal entrance lengths are drastically reduced with increasing wall Reynolds number. This behavior can be used to advantage in the optimal design of grooved, oil-cooled friction pairs such as wet clutches.