Embryonic axes and cotyledons of 3 soybean seed lots designated as normal, naturally aged and acceleratedly aged were analyzed for their organic free radical contents. No signals of free radicals were found in ESR spectra from cotyledonary material of the 3 samples investigated. High levels of organic free radicals were observed in the embryonic axes. There were significant differences in the free radical contents of the embryonic axes; the relative values of free radicals were 100, 190 and 170% for samples aged normally, naturally and in an accelerated manner, respectively. These results point to the physiological role of the embryonic axes during natural or accelerated aging of seeds, notwithstanding that the axis is a small part as compared to the cotyledons. Lipid peroxidation in embryonic axes may play an important role in seed deterioration during aging.