Lysozyme, lactoperoxidase and salivary peroxidase inhibit the metabolism and growth of mutans streptococci, but any possible effects on the adherence of these bacteria are unknown. In this study the effects of lysozyme and lactoperoxidase on the adhesion of 3H-labelled Streptococcus mutans (NCTC 10449, serotype c strain) to saliva-coated hydroxyapatite were studied at pH 5.0 and 7.0. Human whole saliva was either lysozyme-depleted and centrifuged, or sterilized and dialysed to achieve no detectable lysozyme and peroxidase activities; this modified saliva was used to form experimental pellicles. The incorporation of lysozyme (50-200 micrograms/ml) to the pellicle caused a significant (p < 0.01) reduction in the adherence of S. mutans without any loss of bacterial viability. Pretreatment of either saliva-coated apatite or S. mutans cells with lysozyme did not change the results but lysozyme bound more readily to bacteria than to the experimental pellicles. Also, lactoperoxidase (10-200 micrograms/ml) reduced significantly (p < 0.001) the adherence of S. mutans but, in contrast to lysozyme, in a dose-dependent way. The strongest inhibition of adhesion was found when both saliva-coated apatite and bacteria were pretreated with lactoperoxidase. This enzyme bound to experimental pellicles in preference to streptococci. A non-specific protein control, albumin, did not block the inhibition by lysozyme or lactoperoxidase. The inhibition of adherence of a serotype c strain of S. mutans to saliva-coated hydroxyapatite is a novel antibacterial mechanism for both lysozyme and lactoperoxidase.