L-Sorbose, a ketohexose isomeric with fructose, is one of a group of hypoacidogenic sugars with potential utility as a sucrose alternative in confectionery. In the present study, Streptococcus mutans and Streptococcus milleri were grown in pure continuous culture under glucose-limited conditions in a chemically defined medium at a dilution rate of D = 0.1 h––1. Such conditions were aimed at simulating those thought to occur in dental plaque. Cultures were exposed to transient excesses of sorbose and/or glucose such as might occur at or inbetween meals. The presence of sorbose did not affect the normal response of S. mutans to excess glucose but, in higher concentrations, it reduced both acid production and growth – possibly via a futile cycle – and the organism began to wash out. Sorbose had no effect on S. milleri, which might give this organism an ecological advantage in plaque exposed to sorbose. Further studies on this potential sugar substitute seem warranted.