The amino acid lysine has been reported to delay cataractogenesis by 'some unknown mechanism'. Lysine and glycine were found to react with glucose at physiological pH and temperature and undergo non-enzymic glycation. The formation of glycated lysine was shown by paper and thin-layer chromatography, HPLC and using an authentic sample of epsilon-fructosyl lysine. Confirmation was made by studies on incorporation of U-[14C]glucose into lysine and glycine. The extent of glycation of lysine was 15.5% in 96 hr and rose to 20% in 20 days. Lysine and glycine alone of varying concentrations lowered the extent of glycation of lens proteins significantly in glucose-treated homogenates of normal lens from humans and goats. Scavenging of intracellular glucose and thereby protecting the lens proteins from excessive glycation appears to be the mechanism of action by which lysine and glycine could exercise beneficial effect on cataract.