The results of a recent study by Whitford et al. [Caries Res 2002;36:256-265] with subjects whose drinking water was fluoridated led to two major conclusions: (1) Compared to the use of a placebo dentifrice, plaque fluoride concentrations ([F]) throughout much of the day are not significantly increased by the use of an F dentifrice but (2) they are positively related to plaque [Ca] (p = 0.0001). The present double-blind, double-crossover study with 16 subjects used the same protocol and was done to: (1) determine the effects of the use of an F dentifrice on salivary and plaque [F] in a community without water fluoridation and (2) further examine the relationship between plaque [Ca] and [F]. Following the use of an F dentifrice or placebo for one week, whole saliva and plaque were collected 1.0 and 12 h after the last use of the products. The study was repeated to include rinsing with a 20 mmol/l CaCl(2) solution immediately before the use of the dentifrices. The CaCl(2) rinse had only minor effects on salivary [Ca] and [F] and none on the plaque concentrations. Unlike the results found in the fluoridated community, all salivary and plaque [F] associated with the use of the F dentifrice were significantly higher than those associated with the use of the placebo. The results suggest that the cariostatic effectiveness of an F dentifrice should be greater in areas without water fluoridation. As noted previously, plaque [F] were positively related to plaque [Ca] (p = 0.0001).