The radicals formed on gamma-radiolysis of L-methionine and its homopeptides (L-methionyl-L-methionine and L-methionyl-L-methionyl-L-methionine) in the polycrystalline state at 77 K and on subsequent warming over the temperature range 77-293 K were identified using the electron spin resonance (ESR) technique. The H-abstraction radicals in the side chain of methionine residue (alpha-alkylthioalkyl radicals) were detected over the temperature range 180-273 K. Over the temperature range 250-273 K decarboxylation radicals were also observed. On further warming to 293 K, the H-abstraction radicals at the alpha-carbon of methionine and of the C-terminal methionine residue in homopeptides were formed. MOPAC 6.0 software package has been applied for spin density calculations in decarboxylation and H-abstraction radicals at the alpha-carbon.