There is a limited number of techniques to reveal the microstructural distribution of hydrogen near a surface or at the exit points of the hydrogen flux from the metal into the gas phase. The most prominent techniques are tritium autoradiography, I ion microprobe experiments, 2,3 Ag-crystal decoration, 4'5 and several nuclear techniques (see, for example, Reference 6). In particular, the Ag-crystal decoration technique 4'5 uses the special activity of atomic hydrogen on a metal surface to reduce Ag ions in AgBr into elemental Ag. It is therefore sensitive to the hydrogen flux across the interface. This Communication describes new variations of the Ag-crystal decoration technique which expand its applicability and make it far easier to use. Also, the need for tedious dark room procedures in the handling of the nuclear AgBr emulsions 4'5 is eliminated. The principle of the present techniques is the reduction of dissolved Ag, Au, and Pd compounds by atomic hydrogen and the subsequent formation of visible elemental metal crystals at surface locations of high hydrogen activity. The samples used in this work were annealed high-purity polycrystalline Ni sheet and single crystal Ni slabs which were electropolished prior to cathodic hydrogen charging (in 0.1 N H2804, i = 10 to 100 mA/cm 2, t 103 S, T = 20 ~ Several areas on each surface were also masked off with acid resistant lacquer (which was removed right after loading) to have "reference areas" which were not exposed to hydrogen.* After hydrogen loading, the surfaces were