Platelet Derived Growth Factor (PDGF) plays an important role during inflammation and wound healing. Objective: The aim was to investigate the expression of PDGF during the early healing phase of replanted teeth with immediate and delayed replantation compared to the normal periodontium using immunohistochemistry. Methods: Fifty-eight roots from six dogs were endodontically treated and extracted to simulate avulsion injury. Teeth that were not extracted were used as non-experimental group. In the immediate replantation group, the teeth were replanted immediately after the extraction while the roots in the delayed group were bench-dried for one hour prior to replantation. The roots and the surrounding structures were harvested after ½, 2, 3 and 4 days observation for immunohistomorphometric evaluation of the percentage of immunopositive cells and the immuno-intensity of the ECM of cementum, PDL and bone. Kruskal-Wallis and Mann Whitney U tests were used for statistical analysis. Results: PDGF was observed in the cells and ECM of all the 3 periodontal structures of the non-experimental group. The percentage bone cell count was significantly lower than cementum at ½ day (P=0.01) and 3 days (P=0.02) delayed replantation group; as well as lower than PDL at ½ day (P=0.01) and 3 days (P=0.00) immediate and ½ day (P=0.00) delayed replantation groups. There was no significant difference among the non-experimental and experimental groups at any particular observation time. Conclusion: PDGF was expressed in the 3 periodontal structures of the non-replanted and healing replanted teeth under optimal and adverse condition. This implicated the role of PDGF in the periodontal healing of replanted teeth and that PDGF might up-regulate the paravascular progenitor cells during healing process. Acknowledgment: This study was supported by NUS Faculty Research Grant R224-000-018-112.