a secondary ion mass spectrometer, interface in an nd'yag laser via an optical fiber, has been used for direct comparisons of secondary ion and laser desorption mass spectra of the same samples the quality of the mass spectra obtained by both techniques is similar. sharp differences in the secondary ion and laser desorption mass spectra are noted, especially in cases where ions are generated through interfacial ion/molecule reactions. examples of reactions observed in secondary ion mass spectrometry but not in laser desorption mass spectrometry are' (i) silver cationization of polycyclic aromatic hydrocarbons using silver powder: (ii) the hydrogenation of heteroaromatic compounds in the presence of silver: (iii) halogen-for-hydrogen substitution. laser desorption of graphite foil, however, yields abundant c/sub n//sup +/ and c/sub n//sup -/ cluster ions, whereas secondary ion mass spectrometry does not. sequential laser irradiation and ion beam analysis have been used for depth profiling of samples comprising thin metal/organic/substrate layers. the metal overlayer is removed in a controlled fashion by laser ablation and the exposed surface is analyzed using static secondary ion mass spectrometry