The effect of a chemically heterogeneous surface pattern on the microscopic phase separation of a thin film composed of a binary polymer blend has been studied using a three-dimensional self-consistent field method and a Monte Carlo method based on the "bond fluctuation model." The surface motif can be transferred from the surface into the polymer bulk to a depth of several nanometers, and such transfer alters the morphology of the bulk phase. The presence of the surface motif weakens the repulsion between unlike species and improves the miscibility of the blend. Miscibility enhancement is maximized when the characteristic area of the surface motif is comparable to the area of a polymer coil in the bulk. Blends containing semirigid chains are slightly more effective in the transfer of a surface pattern, but the effect on miscibility is significantly smaller.