In the present work, the effects of gamma radiation on solid butylated hydroxytoluene (BHT), which is used as an antioxidant, were investigated by ESR spectroscopy. While unirradiated BHT presented no ESR signal, irradiated BHT exhibited an ESR spectrum with many resonance maxima and minima spread over a magnetic field range of 12 mT and centered at about g = 2.0026. Weak satellite and central intense resonance lines, likely, originated from radical species of different stabilities and ratios were observed to be responsible from experimental ESR spectrum of gamma irradiated BHT. Studies based on the variations of the observed line intensities and spectrum area under different experimental conditions were carried out and characteristic features of the radical species responsible from experimental ESR spectrum were determined. Mesomeric radical species of different stabilities providing to BHT a G value of 0.25 were believed to be induced in gamma irradiated BHT. While species responsible from weak satellite lines were unstable, the species causing central intense lines were found to be relatively stable. BHT belongs to a class of compounds with low radiosensitivity (G = 0.25). This feature of BHT enables the feasibility of radiosterilizations of the products containing BHT as antioxidant without very much loss from its antioxidant benefit. BHT has been shown to provide an opportunity in the estimation of applied radiation dose with a reasonable accuracy if an appropriate mathematical function is used to describe experimental dose-response data. (c) 2007 Elsevier B.V. All rights reserved.