This study presents evidence suggesting that multiple binding sites exist for S. mutans JBP (serotype c) in experimental salivary pellicles formed on hydroxyapatite surfaces. Adsorption isotherms were performed using S. mutans JBP cells at concentrations ranging from 1-1000 (x 10(7) streptococci per mL to pellicles prepared from whole clarified saliva and from saliva which had been previously absorbed with JBP cells. The isotherms were analyzed using a one- and a two-site model. Adsorption of S. mutans JBP cells to pellicles formed from untreated saliva was statistically significantly better described by the two-site model, and the two classes of binding sites present had widely different affinities. Also, there were approximately one-third fewer high-affinity sites than low-affinity sites. In contrast, adsorption of S. mutans JBP cells to pellicles formed from JBP-absorbed saliva was better described by the one-site model, and the sites present were of low affinity. Thus, the absorption process appeared to remove or alter specific salivary molecules which comprise the high-affinity binding sites for S. mutans JBP cells.