A total of 21 pulps were collected from 12 inflamed and 9 normal cases. SOD activity and MDA content were identified in the normal and inflamed pulpal tissues. In the inflamed pulpal tissues, SOD activity and MDA content were significantly increased than those in the normal tissues. The results demonstrated that the inflammation of pulpal tissues resulted in the increasing of the reactivity of superoxide radical and lipid peroxide (LPO). The results also indicated that human dental pulp possessed an endogenous defense mechanism to protect the tissue components from the toxic effects of the reactive oxygen intermediates.