Ethylene was determined by gas chromatography after reaction of radiolytically produced ·OH and O- 2 radicals with methionine, methionine + pyridoxal phosphate and S-adenosyl-methionine (SAM). Both oxygen radicals, alone or in combination, liberate ethylene from methionine and methionine/pyridoxal phosphate. From SAM ethylene was primarily produced by the combined attack of ·OH and H2O2 or O- 2.