Effect of low-energy ion irradiation on plasma membrane permeability has been investigated by using electron spin resonance (ESR) spectroscopy of spin probe technique. The investigated system is plumule cells of wheat (Triticum aestivum L.) seeds implanted by 30keV N+ ions. ESR spectra indicated that plasmalemma permeability is sensitive to low-energyion irradiation. Ion irradiations with increasing fluences up to semi-lethal dose lead to gradual increase in plasmalemma permeability of the plumule cells. The possible factors relevant to the changes in membrane permeability are discussed in relation to the changes in the physical state and chemical nature of membranes.