A computer model has been proposed to be used to calculate the internal friction spectrum, caused by the “diffusion under stress” of hydrogen atoms in a solid solution with a b.c.c. lattice containing substitutional atoms. The model takes into account the long-range pair interaction of dissolved atoms. It is suggested that such interaction acts on diffusion by producing short-range order of mobile hydrogen atoms and by changing their energy. These changes occur in the tetrahe- dral (before the jump) as well as in the octahedral (at the saddle point of the diffusion barrier) interstitial sites and, therefore, produce local changes of the hydrogen diffusion activation energy (the activation energy of internal friction). The relaxation strength is calculated from the local fields of atomic displacements around every atom that participates in diffusion. The model has been used to study the nature of hydrogen relaxation in Ti- and Zr-containing Nb- and V-based alloys and to calculate the “chemical” interaction energy of the H(D)±Ti(Zr) pairs. It was shown that the hydrogen relaxation mechanism in Nb(V)–Ti(Zr)–H(D) alloys consists in diffusion under stress of hydrogen or deuterium atoms in the vicinity of single substitutional atoms at low concentration of substitutional atoms and high hydrogen or deuterium concentration, and in the vicinity of substitutional pairs — at high concentration of substitutional atoms and low hydrogen or deuterium concentration. The “chemical” interaction H(D)–Ti(Zr) in niobium and vanadium is stronger or is of the same order, as the strain-induced (elastic) interaction.