This study was undertaken to evaluate variations in the adsorption of acidic proline-rich proteins to hydroxyapatite seen in different types of saliva. The presence of other proteins in saliva significantly decreased the adsorption of the acidic proline-rich proteins. Adsorption to hydroxyapatite of varying concentrations of two of these proteins, A and C revealed that differences in concentration of acidic proline-rich proteins could at least partly explain the previously observed variations in adsorption. The amount of adsorbed protein decreased with increased concentration of inorganic phosphate. pH and physiological variations in ionic strength had a small effect on the adsorption of proteins A and C.