The expression of immunoreactivities for superoxide dismutases (SODs), Mn-SOD and Cu/Zn-SOD, was immunohistochemically investigated in the lingual periodontal ligament and toe pads of adult rats. Immunocytochemistry for SODs revealed that the axon terminals of both the periodontal Ruffini endings and cutaneous Meissner's corpuscles showed mitochondrial Mn-SOD immunoreactivity, but not cytosolic Cu/Zn-SOD immunoreactivity, indicating Mn-SOD is a useful marker for identifying the mechanoreceptors. It is likely that Mn-SOD in the axon terminals of mechanoreceptors exerts protective action against nerve injury and neuronal death under severe conditions, serving to scavenge free radicals from the axon terminals.