Using the diffusion model previously proposed for solid-state catalytic hydrogenation, it has been possible to show that for a hydrogen isotope exchange reaction resulting in the formation of two or more isotopomers the presence of spillover deuterium (or tritium) gradient in the organic phase induces qualitative alterations in the shape of the kinetic curves which can be used as a criterion of reaction mechanism. For gradient-controlled kinetics the shape of the time dependence plot of the isotopomer ratio Q(RDD)/Q(RHD) must be convex, whereas for uniform concentration distribution this function must be concave. An experimental study of the kinetics of isotopomer formation in the solid-state metal-catalyzed deuteration of glycine has been undertaken, and the results are consistent with gradient-controlled kinetics.