In recent years, there has been renewed interest in the association between DNA damage to the lens epithelium and the development of lens opacities. Although a number ofin vitrostudies have indicated that lens epithelial cells are susceptible to a variety of DNA damaging insults and that these cells posess the capacity to repair such damage, no previous studies have directly addressed whether DNA damage is associated with human cataractin vivo. Utilizing samples of lens epithelial cells obtained from patients undergoing cataract surgery, the percentage of cells containing DNA single strand breaks was directly determined by the single-cell gel assay (SGA) method. Non-cataractous human Eye Bank lenses of similar ages to the cataractous samples and calf lenses were used as controls. In approximately 50% of the cataractous samples analyzed, the proportion of cells containing DNA single strand breaks was significantly higher than in control lenses. No relationship between age and DNA damage was noted. These findings are consistent with the hypothesis that in some human patients with cataract, DNA damage in the lens epithelial cell population may be related to the development of lens fiber cell opacity.