Artificial pellicles were prepared by coating hydroxyapatite beads with whole saliva. Radiolabelled lipoteichoic acid was isolated from Streptococcus sanguis NCTC 7863 by phenol extraction. Various concentrations of radiolabelled lipoteichoic acid were mixed with saliva-coated hydroxyapatite in the presence and absence of high ionic strength phosphate buffer, bovine serum albumin, gelatin, unlabelled lipoteichoic acid, Tween 20 and Triton X-100. The amount of lipoteichoic acid binding was measured by counting the residual radioactivity of the saliva-coated hydroxyapatite after thorough washing. In one experiment the binding was measured in the presence of a mucinous glycoprotein isolated from human saliva. The data were analysed by means of Scatchard and double reciprocal plots of the bound and unbound fraction of lipoteichoic acid. The lipoteichoic acid interacted hydrophobically with the saliva-coated hydroxyapatite; the interaction was complex with multiple binding sites exhibiting a range of affinities. The mean association constant was 1.1 x 10(9) M-1 and the minimum number of binding sites was 3.9 x 10(12)/mm2 of artificial pellicle. The salivary mucin competitively inhibited the interaction, which suggests that this may be one of the salivary components involved.