Adherence to buccal epithelial cells (BEC) and the role played in the binding by lipoteichoic acid (LTA) and other superficial components have been studied in reference and clinical strains of Streptococcus bovis either glucan-positive biotype I or glucan-negative biotype II. To avoid the synthesis of glucan by biotype I strains, adherence was studied in bacteria grown in Todd-Hewitt broth, a sucrose deficient medium. Both biotypes were shown to bind to BEC and clinical isolates, irrespective of biotype attached to the same degree but in greater numbers than reference strains. Inhibition studies suggest that at least two mechanisms,--LTA and protein-mediated--are responsible for the adherence of both glucan-positive and negative strains of S. bovis. Moreover, in glucan-positive strains capsular polysaccharides may be also involved.