Abstract
It is shown that a new type of instability of a non-Fermi-liquid state to the interband scattering of multiparticle excitations can dominate the formation of heavy-fermion states in non-Fermi-liquid metals doped with unstable-valence f impurities. A new mechanism is proposed for the formation of a small energy scale and pseudogaps near the Fermi level in a mixed-valent state.