It has been known for some time that some antibiotics, generally at sub-lethal concentrations, are able to alter the morphology and the shape of bacteria. However, more subtle molecular alterations can also be present, such as disorganization of bacterial surface architecture, which leads to changes in the surface electrical charge that can influence the forces of attraction or repulsion responsible for interaction of bacterial surfaces with environmental surfaces. Bacterial adhesion to epithelial cells is a phenomenon regulated by these mechanisms. Clarithromycin, a new macrolide, at sub-inhibitory concentrations from 1/2 to 1/16 of the MIC, that is to say, from 0.12 to 0.015 microgram/ml, significantly reduces adhesion of Staphylococcus aureus to human buccal epithelial cells. Clarithromycin, as other antibiotics that interfere with the bacterial protein synthesis, should also be able to disturb the synthesis of adhesins. These are ligand molecules located on the surface of bacteria, and thus reduce the ability of bacteria to bind specifically to complementary molecules on the surfaces of epithelial cells which is necessary for host colonization.