Matrix-assisted laser desorption/ionization (MALDI) mass spectrometry has been employed for the evaluation of the glycation level of IgG from healthy subjects and also from well- and badly-controlled diabetic patients. The measurements have been performed on untreated plasma protein fractions. The data obtained have shown that a clear mass increase, originating from non-enzymatic glycation processes, is observed in the case of diabetic patients: for well-controlled ones it is in the range 512-1565 Da, while it becomes 827-4270 Da for badly-controlled diabetic patients. This approach indicates that MALDI mass spectrometry is a highly specific tool that can be employed in the metabolic control of diabetic patients and in studies relating the IgG glycation level to possible immunological impairment.