The emergence of S. mutans in the plaque flora appears to have depended upon the ability of the organism to sequester sucrose from dietary sources, particularly from between-meal, snack-type foods. S. mutans appears to have a pH optimum at about the pH required for tooth solution to begin. This specialization which makes S. mutans cariogenic, also makes it vulnerable to dietary regimens that contain few or no sucrose snacks. As snacks are consumed by youngsters, primarily for pleasure, the use of pleasant tasting sucrose substitutes, that cannot be fermented by the plaque flora and especially by S. mutans, constitutes a viable tactic for caries control. The potential of this approach was demonstrated by the 80 per cent reduction of caries relative to a sucrose control which was observed with a xylitol chewing gum in the Turku study.