There is a growing consensus that altered proteins are more susceptible to degradation than native proteins. The enhancement of degradation of damaged proteins may be of significance since it prevents the accumulation of damaged proteins in cells. Several proteolytic pathways have been discovered in the lens. These include ATP-independent, ATP-dependent and ATP/ubiquitin-dependent proteolytic pathways. However, the extent of involvement of these proteolytic pathways in degradation of damaged proteins is not well described. α-Crystallin was oxidized by exposure to 0·03–3·2 mol · OH (mol protein) −1 . Modifications to the oxidized α-crystallin and proteolytic susceptibility of the oxidized α-crystallin were studied. Exposure to > 0·32 mol · OH per mole of subunit produced aggregates and fragments of α-crystallin. Changes in isoelectric points of the proteins were observed after exposure to 0·64 mol · OH (mol protein) −1 . The extent of loss of tryptophan and sulfhydryl groups was related to the level of · OH-exposure. Carbonyl content increased progressively with increasing oxidation. When incubated with a supernatant of bovine lens epithelial cells, the · OH-modified proteins were proteolytically degraded up to three times faster than untreated α-crystallin. ATP stimulated the degradation of native α-crystallin and α-crystallin which was exposed to 1·6 mol · OH (mol subunit protein) −1 (α1·6). Sixty-seven per cent and 100% of the ATP-dependent degradation of native α-crystallin and α1·6 was ubiquitin-dependent, respectively. The data indicate that α-crystallins oxidized by · OH are recognized and degraded rapidly by cytoplasmic proteolytic systems in bovine lens epithelial cells. Both ATP-independent and ATP/ubiquitin-dependent proteolytic pathways are involved in the degradation of native and oxidized α-crystallin.