The high resolution magnetic sector atom-probe has been employed in a survey of slow field evaporation of most of the transition metals in the presence of hydrogen. No stable hydride ions were seen with W, Pt, Re and Ir whereas either monohydrides or dihydrides or both have been found with Rh, Nb, Mo, Ni, Fe, Cu, Zn, Pd, Zr, Ta, Ti and Au. Multiple hydrides of Cu and Ti are also seen. The appearance of H 3 + ions besides the common H + and H 2 + species, was observed at the surfaces of W, Mo, Pd, Ir, Pt-20%Rh alloy and Ta. The H 3 + ions were most abundant on tantalum and molybdenum surfaces.