It has been customary to explain the dentally beneficial effects of xylitol and certain other polyols in terms of microbiological effects only. The almost complete nonfermentability of xylitol in human dental plaque does contribute to the promising clinical findings that have been obtained both in human and animal trials. The nonfermentability or very low fermentability of xylitol by dental plaque leads to a number of consequential phenomena of possible significance in oral biology. The following are associated with the consumption of xylitol: a decrease in the production of lactic acid; the formation of soluble extracellular polysaccharides which make plaque less adhesive; an increase in the general nitrogen metabolism of dental plaque, this resulting in increased transamination and proteolysis with enhancement of the pool of free amino acids and the possibility of ammonia formation. When these effects are combined with the saliva-stimulating properties of xylitol (common to all sweet carbohydrates), the mechanism of the xylitol effect may be more adequately explained. A number of physicochemical facts have, however, received very little attention. They include the following: xylitol and other polyols strongly protect proteins and enzymes from denaturation; xylitol and other polyols seem to govern the precipitation reactions that occur in saliva or in saturated calcium phosphate solutions. The former reactions may play a role in carbohydrate-induced wound healing and the maintenance of the integrity of the oral defence mechanisms. The latter reactions may manifest themselves in the inhibition of spontaneous precipitation of calcium phosphate; thus these polyols may mimic the function of innate inhibitors, statherin, for example. The total explanation of the xylitol effect may thus comprise aspects that are related both to microbiology and to physical chemistry.