Single crystals of Nα-acetyl L-glutamic acid and Nα-acetyl L-glutamine were γ-irradiated and the paramagnetic species formed were investigated at room temperature by electron spin resonance technique. The observed species in Nα-acetyl L-glutamic acid single crystal were attributed to the, HOOCCH 2 CH 2 C(NHCOCH 3 )COOH radical; and those in Nα-acetyl L-glutamine single crystal to the NH 2 COCH 2 CH 2 C(NHCOCH 3 )COOH and NH 2 COCH 2 CH 2 CH(NHCOCH 3 )COOH radicals. The g values and the hyperfine coupling constants of the unpaired electron with the environmental methylene, methine protons and 1 4 N nucleus were determined.