Streptococcus mutans is believed to be the prime etiologic agent of coronal caries in both humans and animals. It has been suggested that the cariogenicity (virulence) of S. mutans is due to the ability of the organism to adhere to the tooth surface, then colonize or aggregate by synthesizing water insoluble glucans, and produce lactic acid by catabolizing fermentable carbohydrates to demineralize the enamel of teeth. The concept that the initiation of dental caries is associated with the development of sticky (insoluble) glucans has been proposed. A mutant of S. mutans, that was unable to synthesize insoluble glucans, was no longer cariogenic in germfree rats and caries activity was greatly reduced in hamsters. The importance of the glucans in the etiology of dental caries has been reviewed by a number of authors. There is little doubt that the insoluble glucan synthesized from sucrose by S. mutans plays a significant role in caries activity. A second virulence factor characteristic of s. mutans is its ability to produce lactic acid. Some investigators found no significant differences between cariogenic and non-cariogenic streptococci regarding either the amount of lactic acid or other types of fermentation acids produced. Others isolated several mutants of S. mutans that made less lactic acid than the wild type strains and lower caries activity in test animals.