Agaricus bisporus lectin (ABL) isolated from the edible white button mushroom, is composed of two to four very similar isolectins, each a tetramer of approximately 17 kD subunits. This lectin binds the Thomsen-Friedenreich antigen, also called T disaccharide, galactosyl (β-1,3) N-acetylgalactosamine. Unlike peanut agglutinin, which does not bind sialylated T antigen, ABL binds either sialylated or asialylated forms. Also, whereas peanut agglutinin has a proliferative effect on cancer cells, ABL is anti-proliferative, apparently without cytotoxicity. ABL binds all blood groups and O-linked glycans of IgA subclasses. Simple mono- and disaccharides are only marginally inhibitory.