Alterations of electrical properties of human erythrocyte membranes induced by gamma irradiation have been studied by means of conductivity measurements in the frequency range from 10 KHz to 100 MHz. The results clearly demonstrate the role played by haemoglobin in the structural modification of the membrane produced by gamma irradiation. Further support for this point of view has been derived from electron spin resonance measurements carried out on the same samples, labelled with different spin labels which probe the outer half layer of membrane at different penetration levels.