Objective. To examine the distribution of superoxide in the uninflamed and inflamed dental pulp by characterizing the immunoreactivity of the detoxifying antioxidant enzymes, manganese and copper-zinc superoxide dismutases (MnSOD and CuZnSOD, respectively). Study design. In 12 rats, mesial cavity preparations were made on the maxillary right first molar; left molars were unoperated controls. After 5 days, the rats were killed, and histologic sections were processed by using MnSOD and CuZnSOD immunoreactivity, and the extent of inflammation was evaluated on alternate sections stained with hematoxylin and eosin. Results. In the hematoxylin and eosin-stained sections, inflammation was consistent with round-cells: macrophages, lymphocytes, and plasma cells that coalesced into a distinct leukocytic “lesion,” which obliterated portions of the underlying pulp. Both MnSOD and CuZnSOD immunoreactivity increased dramatically in inflammatory cells within the leukocytic lesion and in the tissue surrounding the lesion. Conclusions. The findings suggest that the protective role of SOD increases within pulp cells that are undergoing inflammatory stimulation. SOD immunoreactivity may be an early indicator of stress in pulp. (Oral Surg Oral Med Oral Pathol Oral Radiol Endod 1999;88:488-95)