The Peroxiredoxin (Prdx, Prx, or Trx-Px) family of enzymes is a recently identified family of peroxidases found in free-living organisms. The six known isoforms (Prx1-6) play an important role in protecting lipids, enzymes and DNA against peroxides, such as hydrogen peroxide. The ubiquitously expressed peroxiredoxins have also been shown to play a role in apoptosis and cell differentiation. This is acomplished by the active cysteine of Prx reducing peroxides, which is then converted into a transient cysteine sulfenic acid or cysteine sulfinic acid. If Prx protection is inadequate against peroxidases, the resulting protein and DNA damage may result in neurological disease such as Alzheimer's or DNA damage leading to cancer.