Highly spin-polarized reflection at an interface of a ferromagnetic thin film is made visible by photoelectron spectroscopy. The technique of k-space mapping of the exchange-split Fermi surface is employed to detect standing waves confined to the ferromagnetic layer. A drastic spin asymmetry of this effect is achieved for a specific matching of the Fermi-surface topologies of film and substrate, respectively. For Fe͑110͒ films on a W substrate, intense standing waves are obtained exclusively for majority states, while minority states are virtually unaffected by the boundary.