The structural proteins in the eye lens (ie. crystallins) are amongst the oldest proteins in the body. Changes to the crystallins accumulate with age. Other modifications are associated with the formation of cataract. The nature of these post-translational modifications is unknown. Mass spectrometry should provide an ideal tool for mapping the changes that occur in crystallins as a function of age and during the onset of cataract. The crystallins are comprised of three main classes, alpha (2 subunits), beta (6-7 subunits) and gamma (6 subunits). Within these classes of crystallin there is a high degree of homology, hence sophisticated separation strategies are required for isolation of individual subunits, especially for beta and gamma-crystallins. We have shown that a combination of gel permeation chromatography and fast performance liquid chromatography allows the isolation of individual subunits (eg. beta-B2, gamma-s and alpha-A). In order to establish a baseline of unmodified crystallins, foetal lenses are being examined. We are currently developing on-line HPLC-MS for characterising foetal lens crystallins. Preliminary data for both the foetal proteins and those obtained from multi-step separations of cataractous lenses will be presented and compared. An approach to characterisation of proteins from cataractous lenses will be presented.