Recent studies have indicated that the attachment of bacteria to mucosal surfaces is the initial event in the pathogenesis of most infectious diseases due to bacteria in animals and humans. An understanding of the mechanisms of attachment and a definition of the adhesive molecules on the surfaces of bacteria (adhesins) as well as those on host cell membranes (receptors) have suggested new approaches to the prevention of serious bacterial infections: (1) application of purified adhesion or receptor materials or their analogues as competitive inhibitors of bacterial adherence; (2) administration of sublethal concentrations of antibiotics that suppress the formation and expression of bacterial adhesins; and (3) development of vaccines against bacterial surface components involved in adhesion to mucosal surfaces. Progress has already been made in the development of antiadhesive vaccines directed against the fimbrial adhesins of several human bacterial pathogens.