Two series of experiments, one in hamsters the other in rats, were conducted to compare the dental caries conduciveness of sucrose with that of several other sugars and carbohydrates. Hamsters and albino rats fed a diet containing 56% sucrose in the form of confectionery sugar developed highly active carious lesions in their molar teeth. The lesions were located on “smooth surfaces” as well as in crevicular areas. Fructose, dextrose, maltose, hydrogenated starch, sorbitol, and mixtures of starch were used as substitutes for the sucrose product. In hamsters, which are more prone to experience smooth surface caries, the substitutes used were followed by a reduction in plaque accumulations, less active progression of lesions, and little or no new lesion incipience. In the rats, which are susceptible to a wider variety of lesions, almost all the sucrose-free substitutes were associated with less active cavitation in crevices and on buccal, lingual, and proximal surfaces. However, only the hydrogenated starch product, which is fermented more slowly than the sucrose, was not conducive to circumferential lesions, but it was associated with a low grade form of activity in crevicular areas (sulci).