The adherence of $^{3}H$-labeled oral streptococcal cells to protein-coated hydroxyapatite (HA) beads was studied by a standard adherence assay. The adherence equilibrium for S. mutans 10449 occured in about 2 hrs. The cell numbers adhering to SHA was 50% less than those on bare HA. Sailva from different subjects had varying effect on bacterial adherence. The use of saliva adsorbed with homologouis bacteria decreased S. mutans adherence by 38% ; this indicates the presence of salivary agglutinin in acquired pellicle formed on HA. Animal sera and BSA decreased S. sanguis adherence. BSA concentration as high as 10mg/ml caused up to 87% adherence inhibition. The desorption experiment of adhered bacteria confirmed the previous reports that the adhesive sites on HA beads for S. mutans were different from those for S. sanguis and that S. mutans could enhance the adherence of S. sanguis but not vice versa.