The effect of fluoride pretreatment upon root resorption after delayed replantation was studied in beagle dogs. Upper and lower incisors were extracted and bench dried for 45 minutes. 1% Stannous fluoride solution, 2% neutral sodium fluoride gel and 1.23% acidulated phosphate fluoride gel were used for the pre-treatment of replanted root surface in the experimental groups. Replantation was done with no treatment in control group. After of an experimental periods 3 weeks, animals were sacrificed by perfusion followed by sample preparation. A histomorphometric method was applied for evaluation of tissue reactions observed in each group under light microscope. Scanning electron microscopic observation was done to find out any different surface topography between groups. The results were as follows: 1. Fluoride-treated groups showed in general the better healing patterns than untreated control group. 2. Comparisons between three experimental groups revealed the general superiority of APF-treated group over the other groups in terms of tissue healing reaction by showing the highest frequency in uncomplicated healing pattern and surface resorption and the lowest in inflammatory resorption, but with no statistical significance(p>.05). 3. Scanning elecron micrographs showed the irregular distribution of resorption cavities and the attached bone of variable size and shape in all groups. 4. It can be concluded that the types of fluoride did not have significant impact on the early tissue reactions after delayed replantation under the condition of the present experiment.