Objective To study the effect of concentrations of glucose on the initial adherence of Streptococcus mutans（S.mutans） to saliva-coated hydroxyapatite（SHA
）, and to compare the initial adherence of S.mutans from caries-active group with that of S.mutans from caries-free group. Methods Each 10 clinical isolates of S.mutans from caries-active and caries-free subjects were used in this study. And S.mutans UA159 was also included in this experiment. SHA was used to simulate tooth surface in oral cavity. S.mutans clinical isolates and strain UA159 were cultured in TPY liquid medium containing 3H-TdR in the same radioactive concentration and glucose in 0.2%, 1.0%, 5.0% concentration. Then grown cells were harvested to produce a suspension. SHA and radiolabelled bacterial suspension（A550 nm=0.52） were mixed for 90 minutes, samples were assayed by using liquid scintillation counter, and binding abilities of strains were evaluated by the count per minute（CPM）. Results The initial adherence ability of S.mutans from caries-active group was higher than that of S.mutans from caries-free group（P
