The metabolism of xylitol in xylitol-sensitive strains (strains whose growth is inhibited by xylitol) and xylitol-resistant strains (growth not inhibited) of oral streptococci was compared. Both xylitol-sensitive and xylitol-resistant strains took up xylitol. In the sensitive cells, the xylitol was probably transported via a phosphotransferase system. This resulted in intracellular accumulation of xylitol-5-phosphate and xylulose-5-phosphate. These metabolites were not detected in the xylitol-resistant strains, which probably transported xylitol via a permease system. It appeared that the resistant strains were able to utilize xylitol as carbon and energy source in the absence of other carbohydrates.