Specific pathogen-free Sprague-Dawley rats infected with Streptococcus mutans MT8148R (serotype c) developed a severe dental caries when fed a diet containing 56% sucrose (diet #2000) . Complete replacement of the dietary sucrose with palatinose, a structural isomer of sucrose, however, resulted in negligible caries induction and plaque accumulation. Replacement of half of the sucrose content of diet #2000 with palatinose induced dental caries; however, the caries score was significantly lower than that induced by diet #2000. No significant reduction in caries development was observed when a quarter of the dietary sucrose was replaced with palatinose.