Generation of the imidazoquinoxaline-type heterocyclic amines in the heated model system composed of glucose/glycine/creatinine in aqueous diethylene glycol was effectively prevented by phenolic antioxidants, butylated hydroxyanisole (BHA), propyl gallate (PG), sesamol, esculetin and epigallocatechin gallate (EGCG) in a dose-dependent manner. Generation of the mutagens in heated-and-dried bonito meat was effectively prevented on pretreatment with EGCG or green tea extract. Electron spin resonance (ESR) studies showed that the heated model mixture of glucose/glycine generated the unstable pyrazine cation radical, and its formation was inhibited by BHA, sesamol and EGCG. ESR-spin trapping studies using 5,5-dimethyl-1-pyrroline N-oxide (DMPO) and N-tert-butyl-alpha-phenylnitrone (PBN) showed that the heated model mixture of glucose/glycine or glucose/glycine/creatinine generated unstable carbon-centred radical(s), and their formation was effectively inhibited by BHA, sesamol and EGCG. It is likely that the unstable free radical Maillard intermediates played an important role in the formation of the imidazoquinoxaline-type heterocyclic amines, and the phenolic antioxidants effectively scavenged the radical species to prevent the mutagen formation.