Cooling a flat plate by evaporation of a volatile liquid from the surface to a laminar boundary layer flow past the plate is theoretically analyzed, taking into account both injection effect due to the vaporization and two-dimensional thermal conduction in the plate, with convective thermal-boundary condition on the other plate surface. The thermal effect of the volatile liquid supply to the plate is neglected and all of the physical properties are assumed to be constant in spite of the changes in concentration and temperature in the boundary layer. Representative calculations were performed for air-water system with various thermal conditions of the plate and flow conditions. The temperature fields and distributions of the local Nusselt and Sherwood numbers are estimated for a parallel flow case. The effects of parameters related to the wall conduction on the injection parameter are discussed. Comparison of results calculated for air-methanol and air-water systems shows that in the former case the injection gives more significant influence on the heat and mass transfer characteristics.