The UV (325 nm) photolysis of atomically-dispersed Rh-I(CO)(2) species supported on an Al2O3 surface in the presence of H-2 causes a reduction process producing Rh-x(0) surface species at 200 K. The Rh-x(0) sites are detected by means of the adsorption of characteristic chemisorbed CO species. The H-H bond is activated by the unstable and coordinatively unsaturated (RhCO)-C-I surface intermediate generated during photodecomposition of Rh-I(CO)(2) The results indicate that mobile Rh-containing surface species are produced photolytically from isolated Rh-I(CO)(2) and proceed to form Rh-x(0) clusters; this phenomenon offers a new method for the control of metal dispersion on supported catalysts.