A three-year, double blind, randomised clinical trial was conducted in Polk County, Florida from 1983-1987. The objective was to compare the effect of four dose levels of sodium monofluorophosphate (SMFP) and a single dose level of sodium fluoride (NaF) on DMFS, DMFT, and DFS Interproximal indices. A total of 8,027 children were examined clinically and radiographically at baseline, and 5,474 children completed the three-year study, which included daily supervised brushing at school. No differences existed at baseline between the five study cells on age or gender distribution, or on any of the dental indices. Results indicated that the 2000 ppm F NaF group had significantly smaller DMFS increment than the 2000 ppm F SMFP group p < 0.005. The 2000 ppm F NaF group demonstrated an 18 per cent (26 per cent for children > 10 years at baseline) reduction in DMFS over the 1500 ppm F SMFP group, the 2500 ppm F group a 15 per cent (19 per cent) reduction, and the 2000 ppm F SMFP a 5 per cent (9 per cent) reduction. Results are strongest in children at greatest risk--older children with previous caries. This study concludes that the anticaries efficacy of SMFP dentifrices rises with increasing fluoride, and that the anticaries efficacy of a 2000 ppm NaF dentifrice is superior to that of a 2000 ppm F SMFP dentifrice, p < 0.005).