Peroxidizing lipids were used to induce the formation of antioxidant radicals. It has been shown by electron spin resonance (ESR) spectroscopy and simulation of the first derivative ESR spectra that the radicals formed by this method are the already known tocopheroxyl radicals. dl-alpha-Tocopheroxyl radicals were formed in relatively high concentration but were rather rapidly destroyed as compared to the dl-delta-tocopheroxyl radicals, which were formed in rather low concentration and were destroyed rather slowly, dl-beta- and dl-gamma-tocopheroxyl radicals reacted in an intermediate way. Autooxidation induction times of the same lipids stabilized with the tocopherols show the well accepted series of antioxidant activities alpha less than beta congruent to gamma less than delta. Their relative antioxidant activity is nicely explained by the ESR experiment: the fast reacting dl-alpha-tocopherol is reacting more rapidly and traps the radicals more thoroughly and is therefore only available as an antioxidant for a short period of time as compared with the slowly reacting dl-delta-tocopherol. dl-beta- and dl-gamma-Tocopherols behave in an intermediate way.