A 3-year, double-blind, randomized caries trial was conducted to evaluate the relative anticaries efficacy of four sodium fluoride dentifrices containing 250 ppm fluoride, 1,000 ppm fluoride in combination with 1% disodium 1-hydroxyethylidene-1.1-bisphosphonate (HEBP), and 1,000 ppm fluoride in combination with 1% disodium azacycloheptylidene-2.2-bisphosphonate (AHBP). As a positive control, a monofluorophosphate dentifrice (1,000 ppm fluoride) was used. At outset 1,161 Icelandic children, 11 and 12 years of age, were randomly assigned to one of the five treatment groups and 1,035 subjects completed the trial. After 3 years of unsupervised brushing, the dentifrice containing 250 ppm fluoride was significantly less effective in controlling the caries increment. The combination of sodium fluoride and AHBP was significantly more effective than the positive control.