S ODIUM FLUORIDE applied topically to the teeth gives approximately 40 percent reduction in the incidence of dental caries in children (1-3). Other fluoride compounds may be even more effective. Laboratory studies suggest that stannous fluoride is superior to sodium fluoride in reducing the solubility of powdered dental enamel (4-6) and whole tooth sections in weak organic acids (7), and experimental studies in hamsters (8) and rats (9-11) have corroborated these findings. Also, there are reports of approximately 60 percent reduction in dental caries in children when stannous preparations were used (12-14). The present study has tested further the effectiveness as dental caries preventives of 2 percent stannous fluoride and 2 percent sodium fluoride. Nearly 600 children 9-14 years old in Milwaukie and Oregon City, Oreg., participated in all phases of the 16-month study. The children were divided into two comparable groups, one group receiving stannous fluoride and the other sodium fluoride.