The carbohydrate binding specificities of the leukoagglutinating phytohemagglutinin (L-PHA) and erythroagglutinating phytohemagglutinin (E-PHA) lectins of the red kidney bean, Phaseolus vulgaris, have been investigated by lectin-agarose affinity chromatography of Asn-linked oligosaccharides. High affinity binding to E-PHA-agarose occurs only with biantennary glycopeptides containing 2 outer galactose residues and a residue of N-acetylglucosamine linked beta 1,4 to the beta-linked mannose residue in the core. This species is not retarded on L-PHA-agarose. In contrast, tri- and tetraanternnary glycopeptides containing outer galactose residues and an alpha-linked mannose residue substituted at positions C-2 and C-6 are specifically retarded on L-PHA-agarose. Triantennary glycopeptides containing outer galactose residues and an alpha-linked mannose residue substituted at positions C-2 and C-4 are not retarded on L-PHA-agarose. Additionally, the presence of outer sialic acid residues or a core fucose residue does not influence the behavior of complex glycopeptides on either of these lectin-agarose conjugates. This ability of E-PHA and L-PHA to discriminate between Asn-linked oligosaccharides with various branching patterns can be utilized in the fractionation of these glycopeptides (see paper following).