Three lectins have been isolated from an extract of mistletoe (Viscum album) by affinity chromatography on partially hydrolysed Sepharose and human immunoglobulin- Sepharose. The lectins differ in molecular weight and sugar specificity (lectin I, mol.wt. 11500, D-galactose-specific; lectin II, mol.wt. 60000, both D-galactose- and N-acetyl-D-galactosamine-specific; lectin III, mol. wt. 50000, N-acetyl-D-galactosamine-specific). All three lectins react with human erythrocytes without specificity for the A, B, and O blood groups. In contrast with abrin and ricin the mistletoe lectins cannot be divided into "toxins" and "haemagglutinins".