The effect of the presence of fluoride in toothpaste on tooth wear was investigated in extracted human premolar teeth collected from two geographic areas with different fluoride concentrations in the public water supply. Nine teeth from each area were divided bucco-lingually into matched pairs and subjected to a wear regime in vitro. The regime consisted of 5 minutes immersion in 6% citric acid buffered at pH 3.5, followed by 200 cycles of linear tooth-brushing in a slurry of either a fluoride or a non-fluoride toothpaste, the whole process repeated 720 times. Teeth collected from subjects in Birmingham (public water supply fluoridated at 1 ppm) had a higher fluoride concentration in the surface enamel (P < 0.01) and greater hardness (P < 0.001) than teeth collected from subjects in London (non-fluoridated water supply). The results showed that less wear was produced in the presence of the fluoride toothpaste than in the presence of the non-fluoride toothpaste with an otherwise identical formulation (P < 0.001), and that the amount of tooth wear in vitro was not significantly affected by differences in fluoride concentration and hardness of enamel.