Samples of egg shell powder were annealed in air in the temperature range 298-1173 K. Samples were analyzed by X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy, thermogravimetric analysis and electron spin resonance (ESR). ESR measurements were made on annealed egg shells before and after gamma irradiation at 4 kGy. Annealing egg shells produced a range of organic radical with g-values from g = 2.005 to 2.002. The thermal dependence of this signal may provide valuable information about the extent of the thermal treatment that the sample was subjected to. Samples irradiated from 3Gy to 10 kGy were analyzed by ESR in order to obtain the response curve and to show ESR signal behavior. (C) 2005 Elsevier Ltd. All rights reserved.