A cariogenic bacterial strain, Streptococcus mutans OMZ 176, was found to be able to take up xylitol by a phosphotransferase system (pts) in spite of lack of ability to catabolize this pentitol. A metabolite with an Rf value in TLC similar to xylitol 5-phosphate was extracted from resting cells which had been exposed to 14C xylitol. Phosphatase treatment of this metabolite yielded xylitol. It is suggested that the inhibition of growth of Strep. mutans observed in several laboratories can be explained in terms of accumulation of xylitol phosphate (presumably xylitol 5-phosphate) inside the cells. It is furthermore suggested that xylitol is transported and phosphorylated through the fructose pts.