Radiobiological studies were carried out with three strains of Listeria monocytogenes . Resistance characteristics were determined under a variety of conditions. For one strain (CFPDC), the D10 values were 0.18, 0.21, and 0.44 kGy when subjected to gamma irradiation in phosphate buffer (pH 7.0), trypticase soy broth containing yeast extract (TSB-YE), and in poultry feed, respectively. For this strain, D10 values in poultry feed determined by using 60Co gamma rays or 10 MeV electrons as radiation sources were almost identical. D values for gamma irradiation of TSB-YE cultures were 0.21, 0.25, and 0.46 kGy for CFPDC, Scott A, and 81-861 strains, respectively.