Human alpha-1 acid glycoprotein (orosomucoid, AGP) is a well known acute-phase protein, whose serum concentration rises in patients with injury, infection, inflammation and tumorous growth. The isolation of AGP started from investigations of the seromucoid fraction of human plasma containing carbohydrate-rich protein-like substances that were not precipitated by sulphosalicylic or perchloric acid. AGP has some unusual properties: 45% carbohydrate, 12% sialic acid, isoelectric point of 2.7, molecular weight 41 kD. AGP has five glycosylation sites at which di-, tri- or tetrabranched oligosaccharide chains (antennal structures) are attached to the polypeptidide backbone. AGP displays polypeptide and oligosaccharide chain-dependent microheterogeneity, detected by a number of branched oligosaccharide chains and by sialic acid residues. Oligosaccharide microheterogeneity is determined by crossed affino-immunoelectrophoresis (CAIE). In this case the interaction of AGP with lectins, especially with concanavalin A (Con A), has been demonstrated. The number of sialic acid residues is examined by isoelectric focusing and by capillary electro phoresis. The aim of many authors is to improve the electrophoretic methods for the assessment of AGP glycoforms using additional lectins. The goal to find a relationship between variation of AGP microheterogeneity from electro- phoretic data and the clinical stage of the patient is foreseen for the near future. Recent papers indicate that more information than assessment of the total quantity of AGP will be provided by the control of its microhete- rogeneity.

        Key words: alpha-1 acid glycoprotein, orosomucoid, microheterogeneity, gel electrophoresis, isoelectric focu- sing, crossed affino-immunolectrophoresis, capillary electrophoresis, lectins.