A phosphoenolpyruvate-dependent sucrose phosphotransferase system (PTS) has been demonstrated, by an enzyme-coupled reaction and product isolation, in decryptified cell suspensions of the cariogenic microorganism Streptococcus mutans NCTC 10449. The apparent sucrose PTS reaction for sucrose-adapted, sucrose-challenged cells displayed saturation kinetics with an apparent Km of 7.14 x 10(-5) M, which was distinct from the Km of the glucose PTS activity of glucose-adapted, glucose-challenged cells. Both the sucrose and the glucose PTS activities appear to be inducible and under separate genetic control. The sucrose PTS reaction demonstrated in decryptified cells had an absolute requirement for phosphoenolpyruvate. Only 2-phosphoglycerate, the immediate glycolytic precursor of phosphoenolpyruvate, was found to substitute for phosphoenolpyruvate in this reaction in the absence of fluoride. The sucrose PTS activity of sucrose-adapted cells was competitively inhibited by raffinose and lactose; these same sugars had no effect on the apparent glucose PTS activity. Fructose was the only carbohydrate tested other than sucrose which elicited an apparent PTS reaction in sucrose-adapted cells. The product of the sucrose PTS reaction was isolated and behaved chromatographically on a Dowex-1-X8 column like a monophosphate ester. Alkaline phosphatase treatment of the presumptive sucrose monophosphate liberated a component which behaved chromatographically like free sucrose. Subsequent acid hydrolysis of this component produced moieties which behaved chromatographically like glucose and fructose.