Enterococcus faecalis is a pathogen that persists in medicated root canals. Here, we tested the hypothesis that the E. faecalis proteases, serine protease and gelatinase, and the collagen-binding protein (Ace) contribute to adhesion to the root canal. Scanning electron microscopy was used to examine dentin binding by four E. faecalis strains: OG1RF, the wild type, and three mutant derivatives of OG1RF, TX5128, TX5243 and TX5256 deficient in serine protease and gelatinase, serine protease, and Ace, respectively. For each strain, 20 root halves were exposed to 3 x 10(9) to 5 x 10(9) cells/ml for 6 h, and 50 fields per root half were examined for adherent bacteria. Statistical analysis revealed that adherence of OG1RF was significantly greater than the mutant strains (P < 0.001), while significant differences were not detected between the protease mutants. The data indicate that serine protease and Ace aid E. faecalis binding to dentin, while the role of gelatinase is uncertain.