Human cataract lens proteins can be bleached by exposure to sodium borohydride (NaBH4), sodium cyanoborohydride (NaCNBH3), or hydrogen peroxide (H2O2). The decolouration resulting from these treatments could be monitored by a change in absorbance at 350 nm. At pH 12 the magnitude of the absorbance change increased in proportion with the severity of the nuclear cataract in the case of NaBH4 and H2O2 treatments, but not in the case of NaCNBH3 treatment. The rate of change in absorbance at 350 nm following exposure to the different reagents was used to evaluate three model systems for senile nuclear cataract. These model systems utilized calf lens proteins which had been tanned by exposure either to 3-hydroxyanthranilic acid, dopa/tyrosinase, or ultraviolet light.