AbstractEnthalpy calculations, based on Miedema's model for alloy formation, show theδ–hydride (ZrH~1·6) to be the most stable hydride in the Zr–H system. Theγ–hydride (ZrH) is the least stable and, as suggested in the literature, is quite probably metastable. In addition, theε–hydride (ZrH2±x) is shown to be the last hydride formed in the Zr–H system. TiH1·38is shown to be the most stable hydride in the Ti–H system corresponding to theγ–hydride phase on the equilibrium phase diagram.MST/187