The present study surveyed the ability of 21 strains of cariogenic streptococci of the "mutans" group to bind to human type 1 collagen adsorbed on hydroxyapatite (HA) surfaces. All strains of Streptococcus cricetus (serotype a) and Streptococcus rattus (serotype b) tested attached strongly to collagen-treated HA (C-HA). Streptococcus mutans strains of serotype c and Streptococcus sobrinus strains of serotype d or g attached poorly; or not at all, to C-HA. S. mutans strains OMZ-175 (serotype f) and B14 (serotype e) were exceptions which exhibited significant binding to C-HA. Binding of S. cricetus AHT and S. rattus LB-1 to C-HA occurred in a dose-dependent manner, and was specific since it was inhibited by the presence of soluble collagen, but not by egg albumin, or by human fibrinogen or fibronectin. Binding occurred maximally between pH 6 and 8 and was not affected by any of several sugars tested. Trypsin treatment the streptococci had little affect, but heating at 100 degrees C reduced their ability to bind to C-HA.