Phaseolus vulgaris lectin (PHA-L) is an affinity purified lectin made up of four subunits with carbohydrate specificity for complex oligosaccharides. PHA-L is known as leucoagglutinin and has high mitogenic and leucoagglutinating activity, and low erythroagglutinating activity. This lectin exhibits no agglutination with human erythrocytes. PHA-E differs from PHA-L in that the leucoagglutinin reacts strongly with Tamm-Horsfall glycoprotein and reacts weakly with porcine thyroglobulin. PHA-L binds to fetuin but does not precipitate the glycoprotein. This lectin is strongly inhibited by trisaccharide Gal ?(1,4)GlcNAc?(1,2)Man, and although this structure is present in many glycoproteins, PHA-L does not react with all of them. This lectin reacts strongly with certain carcinoma cell lines of high metastatic potential and has been proposed as a probable therapeutic agent. It has shown potential to inhibit graft vs. host reaction in transplantation studies and has also shown to promote the production of cytotoxic agents which could be useful in cancer therapy.