Reduced adherence and aggregation were associated with protein alterations in parotid saliva after chronic treatment with the beta-adrenergic agonist isoproterenol. In contrast, saliva from animals treated with the beta-antagonist, propranolol, did not cause such changes; the protein composition of this saliva was similar to that of controls. SDS-polyacrylamide gel electrophoresis of protein in saliva samples before and after they were mixed with 10 mg of spheroidal hydroxyapatite beads (HA), as well as protein adsorbed and recovered from the HA, showed that an acidic, proline-rich protein with a molecular weight of approx. 40,000 was the predominant protein adsorbed. This protein was significantly diminished in saliva from isoproterenol-treated rats. Proteins with molecular weights between 44,000 and 48,000 and unique to the saliva from isoproterenol-treated animals were also adsorbed to HA. Thus alterations in proline-rich proteins of parotid saliva may influence the adherence and aggregation of oral bacteria, two processes considered important for in-vivo colonization of oral surfaces.