Glutaredoxin catalyzes glutathione-dependent disulfide oxidoreduction reactions in a coupled system with NADPH, GSH and glutathione reductase and has an active site disulfide/dithiol with the sequence -Cys-Pro-Tyr-Cys-. Calf thymus glutaredoxin (thioltransferase), which contains two additional structural half-cystine residues, was purified to homogeneity, using a modification of the previously described isolation procedure. This method involved a pI-shift of glutaredoxin, obtained after oxidation of the fully reduced form with hydroxyethyl-disulfide, followed by CM-Sepharose chromatography. On both SDS- and IEF-gels the protein migrated as one band (M(r) 12,000). The pure protein was used to affinity-purify rabbit antiglutaredoxin antibodies obtained by immunization with the oxidized form of glutaredoxin. Using these antibodies the distribution of glutaredoxin was mapped in calf organs and tissues by Western blots and by immunohistochemistry. Glutaredoxin was demonstrated in all organs investigated. Western blots showed the presence of weak additional high molecular weight bands of unknown identity in certain organs. The immunohistochemical analyses revealed that glutaredoxin is highly expressed in a wide variety of cell types, both epithelial and mesenchymal. The distribution and occurrence in the calf organs was similar to that previously described for thioredoxin in the rat. There were some exceptions: e.g., follicular cells in the ovary did not contain immunohistochemically demonstrable glutaredoxin but expressed thioredoxin. Particularly striking were observations of strong glutaredoxin immunoreactivity in oocytes in the ovary and the pattern of glutaredoxin in epithelial tissue of the skin and tongue reflecting differential expression during cell differentiation. The distribution demonstrated that glutaredoxin serves functions apart from the originally described role as hydrogen donor for ribonucleotide reductase which only occurs in replicating cells. Such functions should relate particularly to glutathione-catalyzed protein disulfide oxidoreductions and cellular signalling by redox regulating mechanisms.