Electronic structures of small Ni, Pd, and Pt clusters containing atomic hydrogen have been calculated by the SCF Xα SW method, including relativistic effects. Hydrogenmetal bonding is dominated by d-orbitals for Pd and Pt and s-orbitals for Ni, consistent with photoemission spectra for hydrogen chemisorbed on and dissolved in these metals. The results, in conjunction with the concept of orbital electronegativity, suggest why hydrogen solubility and catalytic reactivity vary among these metals.