The role of hydrophobic interactions in the attachment of bacteria to oral surfaces was investigated. Experimental data suggest that S. salivarius and S. sanguis but not S. mutans strains attach to human mucosal cells by the hydrophobic moeity of their lipoteichoic acids. The observations that S. salivarius and S. sanguis adsorbed much better to polystyrene surfaces than S. mutans also supports a strong tendency for these bacteria to undergo hydrophobic bonding. Coating of polystyrene surfaces with clarified human saliva reduced S. mutans adsorption to very low levels whereas S. sanguis still showed significant but reduced adsorption. Similar results were observed in experiments using saliva-coated hydroxylapatite beads. The results suggest that the hydrophobic and electrostatic potentials of the bacterial cell surface and of the saliva formed pellicle influenced the order and strength of adsorption of the bacteria to the test surfaces.