An analysis is performed to study the laminar boundary layer flow over a porous flat plate with injection or suction imposed at the wall. Two different analyses techniques are used for the solution of boundary layer equations: similarity solution and numerical solution. The effect of uniform suction/injection on the heat transfer is discussed. The constant surface temperature thermal boundary condition is used for the horizontal flat plate. The effect of Prandtl number on heat transfer is also investigated. A scale analysis is performed to get more insight into the Prandtl effect. Friction coefficients and Nusselt numbers are calculated for constant fluid injection/suction along the plate. The results indicate that the suction enhances the heat transfer coefficient while injection causes a decrease in heat transfer. (C) 2003 Elsevier Inc. All rights reserved.