A thermal luminescence spectrum of solid lysine in O-2 with an emission peak at similar to 600 nm was measured at 450 K with a Fourier-transform chemiluminescence spectrometer. No emission bands were observed for lysine in N-2, nor its monohydrochloride in O-2 or N-2, under the same experimental conditions. This observation led us to the conclusion that the intermolecular interaction between the free NH2 group on the side chain of lysine and O-2 molecules plays an essential role in this thermal luminescence. This scheme was given support by the finding that the dicyclohexylamine salt of phenylalanine, which has a free NH2 group, but not phenylalanine itself, showed similar thermal luminescence in O-2. (C) 2010 Elsevier B.V. All rights reserved.