With the help of thin layer chromatography, human saliva was examined after varying lengths of incubation time of radioactively labelled xylitol to determine whether bacteria of the human oral cavity are able to use this sugar substitute. This showed that different activities occur in saliva which either complete the breakdown within a few hours or require more than 24 hours incubation. Induction of the enzymes for xylitol and sorbitol breakdown was observed during incubation, which led to a speeding up of metabolism. A comparison with sorbitol revealed that xylitol is metabolised considerably more slowly than sorbitol.