The acidic lectin (WBAII) from the winged bean (Psophocarpus tetragonolobus) binds to the H-antigenic determinant on human erythrocytes and to the T-antigenic disaccharide Gal-beta 1,3-GalNAc. Two crystal forms of WBAII were obtained in the presence of methyl-alpha-D-galactose. Form I belongs to space group R3 with unit-cell dimensions a = b = 182.11, c = 44.99 Angstrom and has one dimer in the asymmetric unit. Form II belongs to space group CZ with unit-cell dimensions a = 135.36, b = 127.25, c = 139.98 Angstrom, beta = 95.9 degrees and has four dimers in the asymmetric unit. Intensity data were collected to 3.0 Angstrom and to 3.5 Angstrom from crystals of form I and II, respectively. The structures were solved by the molecular-replacement method using the coordinates of the basic form of winged bean lectin.