In this study, the total fluoride uptake in partially demineralized enamel from in situ brushing with six dentifrice systems was investigated in vivo among 22 panelists. Five dentifrices with different fluoride systems were compared with a placebo control. Two demineralized enamel discs were placed in proximal positions on specially fabricated dentures worn by each participant. Each treatment involved use of the placebo dentifrice for one week, followed by two weeks of twice-daily use of the test dentifrice. The F- contents of the dentifrices were: A = 1000 ppm F as Na2PO3F + 450 ppm F as NaF; B = 1100 ppm F as NaF; C = 1000 ppm F as Na2PO3F; D = 1000 ppm F as SnF2; E = 1500 ppm F as Na2PO3F; and P = 0 ppm F (placebo). The F- uptakes from A, C, D, and E were not significantly different from each other but were all significantly higher than the placebo. Statistical analysis showed a significantly higher F- level from the NaF-based paste B than that from all other systems. No differences existed between mesial-distal specimens; there was no correlation between F- uptake and age. Significant uptake differences were found between panelists with full and partial prostheses.