Seeds of fig produced in Turkey were studied by electron spin resonance (ESR) technique for detection purposes. Unirradiated fig seeds (control) exhibited a weak ESR singlet at g = 2.0052 +/- 0.0003 (native signal). Irradiation induced at least one additional intense singlet overlapping to the control signal and caused a significant increase in signal intensity without any changes in spectral patterns. Variation of ESR signal intensity of irradiated samples at room temperature with time in a long-term showed that free radicals responsible from the ESR spectrum of fig seeds were not stable but detectable after 80 days. Annealing studies at five different temperatures were used to determine the kinetic behaviour and activation energy of the radiation-induced radicals in fig seeds. A study on microwave saturation characteristics and thermal behaviour of the ESR singlet (g = 2.0052) in irradiated and unirradiated fig seed samples was also carried out by using ESR technique. These preliminary results indicate that microwave saturation characteristics of the ESR signal at room and low temperatures may be useful method to distinguish irradiated fig seeds from unirradiated ones. (c) 2010 Elsevier Ltd. All rights reserved.