Matrix-assisted laser desorption ionisation (MALDI) mass spectrometry was used, in an attempt to find firm evidence for the structure of the species produced in the thermal oxidative degradation of Nylon 6 (Ny6), at 250 degreesC in air. The MALDI spectra of the products showed the presence of polymer chains containing aldehydes, amides, methyl and N-formamide terminal groups. The aldehydes undergo further oxidation to produce carboxylic end groups. The formation fo azomethines, from the further reaction of aldehydes with amino-terminated Ny6 chains, is also supported by the appearance of specific peaks in the MALDI spectra.