Glycated serum proteins were evaluated with fructosamine (GSP-fructosamine) and thiobarbituric acid (GSP) assays in 60 normal and 60 diabetic subjects. Higher levels of GSP-fructosamine and GSP were found in diabetics in comparison to controls. GSP-fructosamine levels were positively related to GSP values and the other metabolic control parameters. Moreover, the fructosamine assay is sensitive, reproducible, rapid and easy to perform. Thus, fructosamine assay could be a useful method for glycated serum protein evaluation in diabetic patients.