Glycosylation of human serum albumin was conducted by its long incubation with the excess either of D-glucose or D-glucose-6-phosphate at 37 degrees C. The glycosylated fractions were isolated by the cation-exchange chromatography on CM-cellulose. The quantity of glucose bound covalently with protein was determined by thiobarbituric acid. The glucose-modified human serum albumin forms stable adducts with amino acids. These complexes are, evidently, produced as a result of the Schiff's base formation between the carbonyl group of the ketoamine adduct of glucose with protein and primary amino group of amino acid further followed by the Amadori rearrangement.