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A single step column procedure for the separation of chick lens soluble proteins is described. α-, β- and δ-crystallin, which account for 80–90% of the soluble protein are separated using this technique, with little or no cross-contamination between classes, as judged by immuoelectrophoresis. Analysis of the fractions in sodium dodecylsulphate-polyacrylamide (SDS) and isoelectric focusing (IEF) gels in dissociating conditions identifies and characterizes the major α-, β- and δ-crystallin subunits. Fresh lenses from day-old chicks were labelled by culturing in medium containing radioactive amino acids and the synthesis of individual crystallin subunits analysed. In both pulse and pulse-chase labelled lenses at least 70% of the incorporated radioactivity could be assigned to characterized crystallin subunits. Differences were observed in the radioactivity profiles from pulse and pulse-chase labelled lenses when analysed on SDS and IEF gels and some polypeptides showed labelling characteristics typical of post-translational modifications of existing protein chains.