The identification of a synthetic resin is achieved by relatively simple, physical methods; but differentiating one member of a particular group from another -- i.e., n-butyl methacrylate from isobutyl methacrylate -- or revealing the structure of a copolymer is much more compli-cated. Pyrolysis carried out under controlled conditions results in fragmentation characteristic for the examined products; the pyrolysis products are analyzed by gas chromatography. The gas chromatography peaks are identified by means of mass spectrometry. The unknown sample is thus identified by its degradation products. The technique and the analysis of specific resins are described. See AATA 19-956.