Shiga toxin is a potent toxin produced by Shigella dysenteriae type 1 strains. The toxin has three biologic activities--cytotoxicity, enterotoxicity, and neurotoxicity--and one known biochemical effect: inhibition of protein synthesis. It consists of two polypeptide chains, an A chain (molecular weight, 32,225) and a B chain (molecular weight, 7,691). These two peptides associate with a stoichiometry of one A and five B subunits to form the holotoxin. The A chain is responsible for the biochemical effect of the holotoxin: cleavage of the N-glycosidic bond of adenine at nucleotide position 4324 in the 28S rRNA of the 60S ribosomal subunit. The B chain mediates binding of toxin to cell surface receptors. Shiga toxin is the prototype of a family of toxin molecules that have been termed Shiga-like in terms of both structural and functional analysis.