The interaction between two plates coated by adsorbed polymer layers is considered theoretically in the marginal solvent regime. A novel mean-field approach that takes into account the effect of chain ends is proposed. The approach generalizes the well-known ground-state dominance theory. It is shown that the effect of polymer chain ends is important even if there is no specific interaction between the ends and the adsorbing plates. Both cases of polymer layers in equilibrium with a bulk dilute or semidilute solution and of fixed amount of polymer between the plates are considered. In all the cases the effect of polymer chain ends changes the interaction between the plates from an attraction to a repulsion if the plates are far enough from each other. This additional repulsive interaction can be qualitatively interpreted as being due to an ideal-gas pressure of chain ends.