The design and the construction of a pyrolysis mass spectrometer suitable for monitoring metal-organic chemical vapour deposition reactions is reported. The CeO2-catalysed decompositions of Hacac (where acac denotes acetylacetone), Hdpm (where dpm denotes dipivaloylmethane), Ce(acac)4 and Ce(dPM)4 were investigated using this apparatus. The temperature dependence and the inhibition of the catalytic surface (1000-3000 angstrom of CeO2) were also studied.