Combined free and forced convection is experimentally investigated for laminar water flow in the entrance region of a semicircular duct with upward and downward inclinations within +/-20 degrees using the boundary condition of uniform heat input axially. The experiment was designed for determining the effect of inclination (particularly the downward) on the wall temperature, and the local and fully-developed Nusselt numbers at three Reynolds numbers (500, 1000, and 1500) and a wide range of Grashof numbers. For the upward inclinations, Nusselt number was found to increase with Grashof number and the inclination angle (up to 20 degrees), while the effect of Reynolds number was found to be small. For the downward inclination, Reynolds number has a strong effect on Nusselt number and the manner by which it varies with Grashof number. The fully-developed values of Nusselt number agree well in magnitude and trend with theoretical results recently obtained by the authors. (C) 2000 Elsevier Science Ltd. All rights reserved.