The stable (5 x 1) surface reconstruction of Ir(1 0 0) is shown to restructure upon exposure to hydrogen as observed and determined by STM and quantitative LEED. The new phase, Ir(1 0 0)-(5 x 1)-H, consists of defect-free Ir nanowires of up to micrometre length with their lateral order depending sensitively on the details of preparation. The Ir wires can be decorated by Fe on both their sides, so that Fe-Ir-Fe sandwich nanowires are formed. The space between the Ir wires can also be filled completely equivalent to the formation of a Fe4Ir surface alloy. It is speculated how this lateral nanostructuring may be combined with one vertical to the surface. (C) 2004 Elsevier B.V. All fights reserved.