OBJECTIVE A large increase in glycation of crystallins between 1 and 8 months has been demonstrated in lenses obtained from aging rats. The objective of this study was to investigate if an age-associated increase in the levels of any of the phosphorylated and nonphosphorylated sugars in the aging rat lenses could be correlated with this increase. METHODS Lenses were obtained from Sprague-Dawley rats ranging in age from 2 to 20 months. Trichloroacetic extracts of these tissues were analyzed by using 31P-NMR for sugar phosphates and high-pressure liquid chromatography equipped with an electrochemical detector for sugars and polyols. RESULTS Although no elevation in the lenticular glucose levels was observed, an age-associated increase in the concentrations of polyol pathway-associated metabolites--sorbitol, fructose, sorbitol-3-phosphate, and fructose-3-phosphate--was detected. In contrast, no significant changes were observed in glycolytic or pentose shunt metabolites. CONCLUSIONS Aging lenses accumulate increased concentrations of fructose and fructose-3-phosphate. Because fructose-3-phosphate is a potent glycating agent and a potential in vivo source of 3-deoxyglucosone, its accumulation in the lens, along with fructose, may be a contributing factor in the age-associated increase of nonenzymatic glycation in rat lenses.