Thin-layer chromatography (TLC) of extracts of cells which had been exposed to 14C-xylitol indicated that xylulose-phosphate is produced by the cells in addition to the previously reported xylitol-phosphate. Resting cell cultures of Streptococcus mutans OMZ 176 pretreated with xylitol were exposed to 14C-glucose and glycolytic metabolites identified by TLC of boiling water extracts of the cells. The developed TLC-sheets showed an accumulation of 14C-hexose-6-phosphates in the xylitol-treated bacteria. This could indicate that a xylitol metabolite, or metabolites, compete with fructose-6-phosphate for the phosphofructokinase, since the glycolysis is inhibited at this step. It was also shown that after accumulation of xylitol-5-phosphate, the bacteria were able to expel xylitol, presumably after and intracellular dephosphorylation of xylitol-5-phosphate; a "futile cycle" is thus present in these cells. Xylitol is taken up and phosphorylated, and at a later step dephosphorylated and expelled. The most important inhibition mechanism was judged to be the competitive inhibition of the glycolysis at the fructose-6-phosphate level.