OBJECTIVE To evaluate the molecular chaperone function of alpha-crystallin with ageing. METHODS alpha-Crystallin of newborn, adult and old rabbits lenses in both of cortex and nucleus were separated by chromatography on Sephacryl S-300HR. The protection of alpha-crystallin against thermal aggregation of catalase and beta L-crystallin (60 degrees C), inactivation of catalase by fructose(37 degrees C) and heat stress(60 degrees C) were measured spectrophotometrically. RESULTS Protection of alpha-crystallin against aggregation and inactivation using four methods showed a similar pattern. The protective ability in cortex was greatly higher than in nucleus of different-aged lenses, and alpha H-crystallin was less than alpha L-crystallin in both cortex and nucleus. There was no statistically decrease with age of chaperone function of both alpha H-crystallin and alpha L-crystallin in the cortex, whereas alpha L-crystallin in the nucleus was compromised. CONCLUSIONS alpha-Crystallin in the nucleus shows age-related decrease in chaperone function, which may be responsible for cataract formation.