A 36-month double-blind clinical caries study was conducted to determine the comparative anticaries efficacy of sodium monofluorophosphate (MFP) and sodium fluoride (NaF) as incorporated in dentifrice formulations. The test dentifrices which were utilized are commercially available in the United States and all have been granted the American Dental Association Seal of Acceptance for anticaries efficacy. The study was conducted in accordance with the 1988 Guidelines of the American Dental Association Council on Dental Therapeutics. The two formulations used in the NaF versus MFP comparison were Colgate Winterfresh Gel with 0.76% sodium monofluorophosphate in a silica base and Crest Regular Flavor Toothpaste with 0.24% sodium fluoride in a silica base. A third commercially-available NaF dentifrice, Colgate Junior Toothpaste with 0.243% sodium fluoride in a silica base, was included in the study for further comparison. Schoolchildren residing in Maine, U.S.A. received a baseline caries clinical examination and then were randomly assigned to the twice-daily use of one of the three dentifrices which were purchased in the marketplace and repackaged in plain white tubes. Caries clinical examinations were subsequently conducted after 2 and 3 years' use of the dentifrices. A total of 2,222 children participated in both the 2 and 3-year caries clinical examinations. The 36-month DFS (decayed and filled surfaces) and the DFT (decayed and filled teeth) mean caries increments for the three dentifrice groups were virtually identical. The children using the MFP formulation experienced a DFS of 1.50 and a DFT of 1.08; those using the Crest NaF formulation experienced a DFS of 1.48 and a DFT of 1.07; subjects in the third group (Colgate Junior Toothpaste, 0.243% NaF) had a DFS of 1.49 and DFT of 1.06. The statistical evaluation of the data consisted of the calculation of 90% confidence bounds for the ratio of (true) mean increments, in accordance with the 1988 American Dental Association Guidelines. Expressed in the language of the Guidelines, the analyses indicated that, (1) the anticaries efficacy provided by the MFP formulation, (Colgate Winterfresh Gel with 0.76% MFP) is "as good as" that provided by the NaF formulation, (Crest Regular Flavor Toothpaste, with 0.243% NaF), and (2) the anticaries efficacy provided by the one NaF formulation (Colgate Junior Toothpaste, with 0.243% NaF) is "as good as" that provided by the other, (Crest Regular Flavor Toothpaste, with 0.243% NaF).