Backround/Objective: Salivary and plaque fluoride concentrations ([F]) increase during and immediately following the single use of a F rinse and then decline during the next 1-2 h. There is evidence, however, that [F] in samples collected 18 h after once-daily rinsing increase during a 2-week period to reach a plateau and, upon cessation of rinsing, gradually decrease to baseline concentrations (Duckworth et al, JDR 66: 1730ff, 1987). This suggests the possible existence of an intraoral F reservoir that is slow to fill and slow to empty. Our study was designed to provide additional data with which to evaluate this possibility. Methods: Six adults avoided the use of F products except for the experimental NaF rinses (0, 226, 1000 ppm F) which were used once-daily before bedtime. The order of rinsing for each 2-week period was: placebo, 226 ppm, placebo, 1000 ppm, and placebo. Saliva and plaque samples were collected on Tuesday and Friday each week 18 h after rinsing. F was analyzed by electrode after HMDS diffusion. The results were analyzed for statistically significant differences using RM ANOVA. Results: Salivary [F] (mg/L) associated with the placebo (n=72), 226-ppm (n=24) and 1000-ppm (n=24) rinses averaged (± SE) 0.030 ± 0.002, 0.039 ± 0.008 and 0.033 ± 0.004 (p=0.28). Dry plaque [F] (mg/kg) averaged 82 ± 7.7, 132 ± 25.7 and 133 ± 35.6, respectively (p=0.05) but no pairwise comparison was statistically significant. Conclusion: The difference between the [F] in the 226-ppm and 1000-ppm rinses was not reflected in the salivary or plaque [F]. Salivary [F] did not reflect the existence of an intraoral F reservoir. Such a reservoir was suggested only by the [F] in plaque from two of the six subjects.