The adsorption and decomposition on polycrystalline Rh of (methylcyclopentadienyl) (1,5-cyclooctadiene) iridium, (MeCp)Ir(COD), has been studied by temperature-programmed desorption (TPD) using time-of-flight mass spectrometry and Auger electron spectroscopy. During early stages of dosing at 100 K there is partial decomposition of (MeCp)Ir(COD) and, in subsequent TPD, only H-2 desorbs. For higher doses, (MeCp)Ir(COD) and H-2, but no hydrocarbons, desorb. The H-2 evolves in several saturable peaks reflecting stepwise C-H bond breaking. In isothermal reaction spectroscopy involving, dosing between 350 and 750 K, desorbing products include hydrocarbons with intensities varying with temperature and dosing time. Total sticking probabilities (S-t) are unity on clean Rh but decrease as deposition products accumulate. Above 750 K the decomposition reaction continues even when the Rh surface is completely covered with precursor decomposition products.