Carbon-carbon bond activation in adsorbed cyclopropane is observed following exposure to gas phase atomic hydrogen on the Ni(100) surface for temperatures as low as 100 K. Exposure to either gas phase atomic hydrogen or deuterium results in formation of adsorbed propyl. In both cases subsequent reaction between adsorbed propyl and coadsorbed hydrogen/deuterium produces propane at 121 K. The activation of a single C-C bond in adsorbed cyclopropane dominates as indicated by the fact that propane is the only product observed. No multiple C-C bond activation which would result in methane or ethane formation was ever observed. These reactions and their mechanisms have been investigated using temperature-programmed reaction (TPR) and vibrational spectroscopy using high-resolution electron energy loss spectroscopy (HREELS). The reactivities of hydrogen and deuterium were indistinguishable during these experiments so we have used the generic term hydrogen or gas phase atomic hydrogen to describe the reactions of both hydrogen and deuterium, The vibrational spectrum of adsorbed cyclopropane indicates weak interaction with the Ni(100) surface at 100 K.