Peroxiredoxins are ubiquitous enzymes that are part of the oxidative stress defense system. In the present study, we identified three peroxiredoxins [bacterioferritin comigratory protein (Bcp)1, Bcp3 and Bcp4] in the genome of the aerobic hyperthermophilic archaeon Sulfolobus solfataricus. Based on the cysteine residues conserved in the deduced aminoacidic sequence, Bcp1 and Bcp4 can be classified as 2-Cys peroxiredoxins and Bcp3 as a 1-Cys peroxiredoxin. A comparative study of the recombinant Bcps produced in Escherichia coli showed that these enzymes protect DNA plasmid from oxidative damage and remove both H(2)O(2) and tert-butyl hydroperoxide, although at different efficiencies. We observed that all of them were particularly thermostable and that peak enzymatic activity fell within the range of the growth temperature of S. solfataricus. Furthermore, we discovered an alternative Bcp reduction system whose composition differs from that of the peroxiredoxin reduction system previously characterized in the aerobic hyperthermophilic archaeon Aeropyrum pernix. Whereas the latter uses the thioredoxin/thioredoxin reductase/NADPH system, this alternative Bcp system is formed of the protein disulfide oxidoreducatase, SSO0192, the thioredoxin reductase, SSO2416, and NADPH. The role of Bcps in oxidative stress was investigated using transcriptional analysis. Different northern blot analysis responses suggested that the Bcp antioxidant system of S. solfataricus can both operate at the constitutive level, with Bcp1 and Bcp4 preventing endogenous peroxide formation, and at the inducible level, with Bcp3 and the already characterized Bcp2 protecting cells from the attack of external peroxides.