Cells MDA-MB-157 isolated from the pleural effusion of a patient with breast cancer will be grown in cell culture and in ascites form in athymic mice. The surface glycoproteins will be obtained by trypsin and papain digestion, purified by gel chromatography, and characterized by physical and chemical determinations: molecular weight, carbohydrate and amino acid components, and structure of carbohydrate chains by periodate oxidation, methylation procedure, and enzymic degradation. The immunological properties and the biosynthesis of the major glycoprotein will be investigated.