The antibody HEB-29 reacts with human blood group B. The specificity of the antibody HEB-29 was confirmed by comparison of specificity and reactivity to standard reagent using >5.000 samples of blood. MAb HEB-29 shows specific staining of erythrocytes and vascular epithelium of blood group B controls and no staining in group A controls. It is applicable for tissue staining in tumor patients with blood groups B and AB. Blood group antigens are generally defined as molecules formed by sequential addition of saccharides to the carbohydrate side chains of lipids and proteins detected on erythrocytes and certain epithelial cells. The A, B and H antigens are reported to undergo modulation during malignant cellular transformation. Blood group related antigens represent a group of carbohydrate determinants carried on both glycolipids and glycoproteins. They are usually mucin type, and are detected on erythrocytes, certain epithelial cells, and in secretions of certain individuals. Sixteen genetically and biosynthetically distinct but inter related specificities belong to this group of antigens, including A, B, H, Lewis A, Lewis B, Lewis X, Lewis Y, and precursor type 1 chain antigens.