The pathogenic potential of Shigella is correlated with the ability of the organism to invade and multiply within the cells of colonic epithelium, Although invasion is the ultimate event, a preceding step is adherence. Shigella dysenteriae 1 preferentially adhered to colonic mucin and not to small intestinal mucin. The pathogen showed a very strong adherence pattern to human colonic mucin when compared with guinea pig and rat mucin, The adherence pattern of S, dysenteriae 1 was not altered on preincubation with monosaccharides present in mucins, suggesting that the receptor for the pathogen is not a simple sugar. Binding of S, dysenteriae 1 to human colonic mucin was not by weak hydrophobic forces. The bacterium also adhered to glycolipids, emphasizing the role of glycoconjugates as receptors for S. dysenteriae 1.