A differential effect on protein synthesis has been demonstrated in the lenses of galactosemic rats. During galactose cataract development the synthesis of lens crystallins is depressed, whereas that of noncrystallin proteins is unaffected. This effect correlates with the influx of Na+ and loss of K+ from the lens. Removal of the galactose diet results in a gradual recovering of crystallin synthesis to normal levels. In vitro the nuclear cataractous lenses leak crystallins into the media; however, upon 5 day's recovery no leak-out of crystallins could be detected. Both decreased synthesis and leak-out probably account for the marked loss of dry weight of cataractous lenses. These results support the hypothesis that crystallin synthesis may be affected by cation imbalance or changes concomitant with such an imbalance.