The production of superoxide dismutase (SOD) varied in Deinococcus radiophilus, the UV resistant bacterium, depending upon different phases of growth, UV irradiation, and superoxide treatment. A gradual increase in total SOD activity occurred up to the stationary phases. The electrophoretic resolution of the SOD in cell extracts of D. radiophilus at each growth phase revealed the occurrence of MnSOD throughout the growth phases. The SOD profiles of D. radiophilus at the exponential phase received oxidative stress by the potassium superoxide treatment or UV irradiation also revealed the occurrence of a single SOD. However, these treatments caused an increase in SOD activity. The data strongly suggest that D. radiophilus has only one species of SOD as a constitutive enzyme, which seems to be a membrane-associated protein.