The use of clays in the treatment of enterocolitis is justified by their ability to adsorb viruses, biliary acids and bacterial toxins secreted into the intestinal lumen. We have studied the in vitro inactivation of the LT toxins of Vibrio cholerae and E. coli, the ST toxin of ETEC and the verotoxin of EHEC. These various toxins were incubated with two types of clays, smectite and kaolin, to investigate the influence of dose, pH variations and the duration of contact of the clays with the toxins. Irrespective of their presence or absence in the supernatant, the biological activity of the toxins was assessed in cell culture and in the newborn mouse test. Both clays inactivated the LT toxin. Smectite was more efficient than kaolin as it was active immediately especially at the pH of intestinal chyme. The LT toxins were adsorbed on the clays by hydrogen bonding. This permitted the segregation of the toxins and prevented them from being fixed to the membrane receptors on the cells. The two clays were ineffective against the verotoxin of EHEC when the pH was alkaline although they were more efficient at acid pH. ST toxin of ETEC was slightly adsorbed by smectite and kaolin.