Objective: To evaluate whether an intact respiratory burst exists within the orbit of diabetics with rhinocerebral mucormycosis. Methods: Immunohistochemical detection of nitrotyrosine in the orbital tissue of diabetics requiring exenteration due to rhinocerebral mucormycosis. Nitrotyrosine is the stable product of the nitration of tyrosine residues by peroxynitrite. Peroxynitrite is a potent oxidant produced by the combination of superoxide and nitric oxide during the respiratory burst. Results: Four specimens were analyzed. All showed focal areas of specific staining against nitrotyrosine of the walls and internal structures of fungal organisms. Conclusions: An intact respiratory burst is present in the orbit of diabetics during infection with rhinocerebral mucormycosis. Possible mechanisms of peroxynitrite's microbicidal effects and reasons for a deficiency in diabetics are discussed.