The thermal decomposition of 1- and 2-propyl iodides on Ni(100) was studied by using temperature programmed desorption (TDP), X-ray photoelectron (XPS), and static secondary ion mass (SSIMS) spectroscopies. Both compounds adsorb molecularly below 100 K but decompose between 100 and 180 K via the dissociation of the C-1 bond, a reaction that requires an activation energy of only about 2 kcal/mol and that yields propyl moieties and iodine atoms on the surface. At low coverages (1 langmuir) the propyl groups generated this way undergo total decomposition to carbon and hydrogen (which desorbs at 350 K), but at higher coverages (3 langmuirs and above) significant amounts of both propylene and propane desorb from the surface as well. Isotope labeling experiments indicate that most of the propane and propylene detected in the gas phase form simultaneously above 150 K as the result of reductive and beta-hydride elimination steps, respectively, but some low temperature disproportionation is observed as well, a process most likely related to the surface chemistry of the propyl iodides themselves. No C-C coupling reactions take place on this nickel surface under the conditions of the experiments.