Streptococcus mutans AHT mutants M1, M2, and M13 failed to adhere to a glass surface, whereas mutants M9 and M35 exhibited decreased and increased adherence, respectively, as compared with the parent strain, when grown in sucrose broth. Extracellular glucosyltransferase prepared from glucose-grown cultures of the adherent strains (wild type, M9, and M35) induced adherence of heat-killed cells of the homologous and heterologous streptococcal strains as well as of Escherichia coli K-12 and uncoated resin particles. The glucosyltransferase was adsorbed on all the streptococcal cells and glucan-coated resins, but not on E. coli cells and the uncoated resins. Glucosyltransferase from the nonadhering mutants (M1, M2, M13) neither was significantly adsorbed on nor induced adherence of any of the cells and resins. Cell-free enzymes from the glucose-grown adherent strains produced water-soluble and water-insoluble glucans, whereas those from the nonadhering mutants produced only water-soluble glucans. Small amounts of alkali-soluble, cell-associated glucan were recovered from the sucrose-grown nonadhering mutants. Thus, the relative proportions of glucosyltransferase isozymes elaborated by the S. mutans mutants, insofar as they affect the physico-chemical properties of the glucans produced, seem to determine the adherence abilities of the cells. The adsorption of glucosyltransferase on glucan molecules on the cell surface is not required for the adherence of S. mutans, but de novo glucan synthesis is important in the adherence process.