Protein-bound glutathione was identified and measured in normal and cataractous human lenses. In a major group of cataracto us lenses the bound glutathione concentration was higher than normal. Study of normal lenses showed that their glutathione content is age-dependent, decreasing steadily from about 3.5mumol/g of lens at age 20 years to about 1.8mumol/g of lens at age 65 years. Cataract brings further decreases.