IN: International Congress of Fluid Mechanics, 3rd, Cairo, Egypt, Jan. 2-4, 1990, Proceedings. Volume 4 (A90-46836 21-34). Mansoura, Egypt, Mansoura University, 1990, p. 1607-1623. This paper presents a computational scheme for flow over a rough surface subjected to a pressure gradient, with the wall function of the scheme modified to account for external pressure variation and surface roughness. It is shown that the flow characteristics predicted by this computational scheme agree well with available experimental data. By performing numerical experiments, an empirical relationship was deduced for predicting rough flow skin friction under pressure gradients. The relationship was tested against other experimental data and alternative empirical formulas, showing good agreement. Keywords: FRICTION DRAG, PRESSURE GRADIENTS, SKIN FRICTION, SURFACE ROUGHNESS EFFECTS, TURBULENT BOUNDARY LAYER, COMPUTATIONAL FLUID DYNAMICS, SHEAR STRESS