A series of experimental studies of the dynamical magnetic response of Sm in SmB 6 -based mixed-valence (MV) systems has been carried out by inelastic neutron scattering on poly-and single-crystalline, double-isotopic ( 154 Sm, 11 B), samples. In addition to two strongly damped high-energy peaks associated with the inter-multiplet transitions of Sm 2Ψ and Sm 3Ψ , pure SmB 6 exhibits a very specific low-energy excitation at 14 meV. These features can be ascribed to the formation of the MV ground state. To study the effect of a variation of the average valence on the magnetic excitation spectra, solid solutions have been studied in which 2Ψ or 3Ψ ions are substituted for Sm. The intensities of the inter-multiplet excitations change roughly in accordance with the variation of . Systematic changes are observed in the position of the low-energy peak and in the Q and T dependences of its intensity, Further information concerning the energy, anisotropy, and the Q and T dependences of the low-energy excitation was obtained from triple-axis experiments on single crystals of Sm 1Ψx La x B 6 (x β«Ψβ¬ 0.10, 0.22) at ambient pressure and SmB 6 at P β«Ψβ¬ 0.5 GPa. The transformations observed in the low-energy part of the spectra suggest a relation between the average valence and the degree of delocalization (or hybridization strength) for the ''loosely bound'' f-electron state formed around the Sm ion, which is a characteristic feature of the MV ground state.