The interaction of hydrogen with the closepacked facets of seventeen transition metals overlaid with 1 ML of five transition metals (Au, Ag, Cu, Pt, and Pd) has been studied using periodic self-consistent (GGA-PW91) density functional theory (DFT) calculations. For noble metal overlayers (Au, Ag, and Cu), hydrogen at the hostmetal/overlayer interface (subsurface hydrogen) is more stable than subsurface hydrogen in the pure host. For certain Au and Ag overlayers, subsurface hydrogen is more stable than surface hydrogen in the same system. The presence of subsurface hydrogen was found to have a significant effect on the electronic structure of the overlayer, resulting in its modified surface reactivity.