Laser desorption/Fourler transform Ion cyclotron resonance mass spectrometry Is found to be a viable method for Identifying polymer additives In polyethylene extracts. Reference spectra were obtained for 18 antioxidants, 7 UV absorbers, and 4 amide waxes. The spectra were found to contain Intense quaslmolecular Ions (Na+ and K+ adducts) and also structurally Informative fragments, depending on conditions used. The molecular weights of several additives In the diethyl ether extracts of three commercial polyethylenes were determined by using the characteristic Na+/K+ adduct pairs observed In the laser desorption spectra. Two additives were Identified as phenolic antioxidants.