A lectin fraction from Chardonnay grape juice has been isolated by affinity chromatography on a column of p-aminophenyl beta-D-glucoside-derivatized agarose. The lectin fractions agglutinate rabbit and human erythrocytes without serological specificity. None of the usual monosaccharides, glycosides, or glycoproteins inhibit the hemagglutinating activity. Erythroagglutination is only inhibited by nitrophenyl glycosides, p-nitrophenyl beta-D-glucoside being the strongest inhibitor. In SDS-PAGE in the presence of 2-mercaptoethanol and gel filtration HPLC, the lectin fraction gave a single band or peak corresponding to M(r) 13.2-11.9 kDa, thus indicating it to be a monomer. Three bands were observed by isoelectric focusing with pI values of 4.1, 4. 4, and 4.9. The isolectins seem to be glycoproteins since they are bound on a concanavalin A-Sepharose column.