Potentially sticky diets were devised containing (a) toffee made from sugar, starch and water, or (b) a viscous sugar syrup. These were compared with diets containing the same ingredients in powder form (45 to 46 per cent sucrose or sucrose + invert sugars), fed to two strains of caries-susceptible rats for 5 or 8 weeks from weaning. The powder diets were significantly more cariogenic than the toffee and syrup diets in the Osborne-Mendel strain of rats, which was highly susceptible to caries, whereas the results with the less susceptible Wistar strain showed no consistent difference between the two types of diet. © 1969.