  We have generalized the Edwards' method of collective description of dense
polymer systems in terms of effective potentials to polymer blends in the
presence of a surface. With this method we have studied conformationally
asymmetric athermic polymer blends in the presence of a hard wall to the first
order in effective potentials. For polymers with the same gyration radius $R_g$
but different statistical segment lengths $l_{A}$ and $l_{B}$ the excess
concentration of stiffer polymers at the surface is derived as $% \delta \rho
_{A}(z=0)\sim (l_{B}^{-2}-l_{A}^{-2}){\ln (}R_{g}^{2}/l_{c}^{2}{)%}$, where
$l_{c}$ is a local length below of which the incompressibility of the polymer
blend is violated. For polymer blends differing only in degrees of
polymerization the shorter polymer enriches the wall.
