Peroxiredoxins are a novel family of antioxidant proteins that specifically prevent enzymes from metal-catalyzed oxidation. The localization of a member of the mono-cystein subfamily of peroxiredoxins, the 28-kDa protein, in different rat tissues and its antioxidant properties were investigated. By immunoblotting, the 28-kDa peroxiredoxin was found to be most highly concentrated in olfactory epithelium and present in all tissues tested (skin, lung, trachea, kidney, womb, and brain). Immunostaining with rabbit polyclonal antibody raised against the 28-kDa peroxiredoxin revealed the particularly high level of the 28-kDa peroxiredoxin immunoreactivity in air-contacting areas (apical regions and mucus of the olfactory and respiratory epithelium and skin epidermis), which are continually exposed to numerous air-borne reactive oxygen species. In the apical regions of the olfactory and respiratory epithelium, the 28-kDa-peroxiredoxin immunogold labeling outlined microvilli and cilia and was mainly located in sustentacular cells and in respiratory and goblet cells, as electron-microscopic analysis revealed. In skin epidermis, the 28-kDa peroxiredoxin immunoreactivity was confined to the granular layer and specifically concentrated in sebaceous glands of hair follicle. In situ hybridization with 33P-labeled antisense RNA probe revealed the expression of the 28-kDa peroxiredoxin mRNA in tissues with a high level of the 28-kDa peroxiredoxin immunoreactivity. Immunodepletion of the 28-kDa peroxiredoxin profoundly decreased the antioxidant activity of the olfactory tissue extract.