173 exfoliated teeth were collected from three groups of children, age 9–10 years, who for three school years used daily one of three mouthrinses consisting of (a) 200 ppm F, 0.1 m phosphate at pH 4.0, (b) 200 ppm F at pH 7.0, or (c) a placebo rinse. The average F concentration at 5 μm in 58 placebo treated teeth was 595 ppm. After approximately 190 rinses, the average F concentration at 5 μm for the pH 7 and pH 4 fluoride rinse groups was 616 and 677 ppm, respectively. The difference between the control and pH 4 rinse was statistically significant. After an initial uptake, further increases in the fluoride concentration of deciduous enamel with continued rinsing was not observed.