Shigella dysenteriae and Shiga-toxin-producing Escherichia call (STEC) elaborate the AB holotoxins, Shiga or Shiga-like toxins (Stx). Stx play a major role in the pathogenesis of haemorrhagic colitis and haemolytic uremic syndrome. This review provides an overview of the mechanisms of action of Stx and a model of the pathogenesis of Stx-induced disease. (C) 2001 Editions scientifiques et medicales Elsevier SAS.