As a consequence of the partial substitution of sucrose by sugar alcohols in the cariogenic diets 580 or 2000, rats often suffer severe diarrhoea, resulting in retarded body weight gains, impaired general health and sometimes high mortality. The purpose of the present study was to develop a more suitable diet to test sugar substitutes, with special emphasis on the general health of the rats and less extreme caries scores in comparison to diet 2000. A purified powder diet (SSP), which meets the nutritional requirements of the rat and containing 50% carbohydrates in which the ratios of starch, sugars and sugar substitutes can be varied, was tested. The results showed that: (1) Streptococcus mutans established well in the oral cavity of the rats; (2) this diet induced reproducible and moderate numbers of carious fissure lesions in S. mutans inoculated rats while non-inoculated animals remain almost caries free; (3) polyols can be added to this diet within reasonable limits without inducing diarrhoea and without influencing body weight gains and general health. In addition it was shown that the partial substitution of starch by xylitol resulted in a statistically significant caries reduction (p < 0.02), both in S. mutans serotype c and serotype d inoculated rats.