Products from the advanced Maillard reaction, which increase during aging and diabetes, may contribute to the development of the typical pathology of aging and diabetes. These compounds are detectable only by their characteristic fluorescence, and few data based on long-term studies are available. For this reason, we studied subcutaneous skin collagen fluorescence in 57 nondiabetic (10- to 110-wk-old) and 74 streptozocin-induced diabetic (10- to 22-wk-old) rats. An exponential increase (r = 0.969, P less than 0.001) of collagen-linked fluorescence (excitation at 370 nm, emission at 440 nm) was observed with aging; after a lag, diabetes induced an earlier dramatic elevation of the fluorescence, suggesting a more complicated phenomenon than simple accumulation. To prevent such increases, the effects of 1 g.kg-1.day-1 aminoguanidine, suggested to be an inhibitor of the advanced glycosylation reaction, and 1 g.kg-1.day-1 rutin, an aldose reductase inhibitor, in drinking water were tested. Both treatments had a significant lowering effect on collagen fluorescence in diabetic rats. The mechanisms by which aminoguanidine and rutin prevent the accumulation of fluorescence are unknown, but these observations raise the question of whether they could be identical. If fluorescence is a marker for age-related pathologies and diabetic sequelae, aminoguanidine and rutin could have therapeutic effects in their prevention.