[en] The T-P diagrams of Ti-H and Ti-D systems were studied at pressures of 25 to 65 kbar, and a marked isotope effect was observed for the minimum pressure when the high-pressure phase appeared. The occurrence of another high-pressure phase is concluded from splitting of one of the transformation lines at P>40 (50) kbar. Transformations of the χ-phase quenched under pressure (χ → κ+Ti → γ+Ti in TiH(D)_∼0.75) were studied at P=1 atm by calorimetric and neutron scattering techniques. A double-peaked exothermal effect evidenced metastability both of χ-and intermediate κ-phases. The hydrogen in the intermediate κ-phase was partially ordered in tetrahedral interstices on alternate {110} planes. Complete H ordering resulted in stoichiometric γ-TiH and precipitation of disperse Ti. Parameters of the transformations exhibited a considerable isotope effect. The γ to α+δ transformation in the Zr-H system is reversible, therefore, γ-ZrH is a stable phase below the transformation temperature. A phase transformation was found in deficient dihydrides, ZrH_1.59 and ZrD_1.69, under pressure. (orig.)