A double-blind clinical study extending over 3 years is reported. Two examiners independently examined 944 subjects to evaluate the efficacy of a calcium carbonate-based sodium monofluorophosphate dentifrice and a similar sodium monofluorophosphate dentifrice but with calcium glycerophosphate as an additive. Subjects brushed only at home withouth supervision. Subjects in booth treatment groups showed a statistically significant lower caries incidence than subjects in the control group. Both independent examiners detected a consistent, though statistically non-significant, trend towards lower caries increments in the group using the dentifrice containing both sodium monofluorophosphate and calcium glycerophosphate. Evaluation of caries incidence according to oral hygiene demonstrated statistically significant greater treatment effect and lower caries incidence with better oral hygiene. Although the examiners had not been calibrated, close agreement between their independent findings is shown.