Electron paramagnetic resonance (EPR) spectroscopy was applied to the studies on free radicals in wheat grains. The stable free radicals normally present in cereal grains can be detected by EPR measurements. Concentrations of the radicals in investigated grains were in the order of 1016 spins/gram of dry mass. The single signal characteristic for oxygen-containing (semiquinone) radicals at g=2.0047 was observed as a dominating EPR signal; a small admixture of an additional radical at g=2.006 was also detected. The He-Ne and semiconductor laser irradiadion of the grains (doses 10-5 to 10-1 J/cm2) resulted in a distinct increase of the stable radical concentration (signal at g=2.0046). The increase of 10 to 30% depending on the laser irradiation technique was measured; the dependence on the dose and the cultivar was less significant. The new radicals have transient character and EPR signal of the laser irradiated grains gradually decreases for several days to stabilize at the normal level of the radical concentration.