Purpose: The collection of autologous platelet-rich plasma (PRP) has demonstrated favorable affects on wound healing in compromised patients. The purpose of this study was to evaluate the expression of PDGF, bFGF, and TGF-b in irradiated and nonirradiated bone in a rabbit tibia model and the ability of PRP to increase growth factor expression when added to autogenous bone graft in a rabbit cranial defect model. Materials and Methods: Ten New Zealand White rabbit tibiae and calvariae were utilized for this study. Tibiae were irradiated at 60 to 70 cGy and evaluated for expression of PDGF, bFGF, and TGF-b. Rabbit calvariae were also analyzed after grafting with autogenous bone and PRP for determination of growth factor expression. Results: Decreased expression of PDGF, bFGF, and TGF-b was seen in cortical and cancellous bone samples when irradiated bone was compared to nonirradiated rabbit tibiae. An increase in PDGF, bFGF, and TGF-b expression was detected in cortical autogenous bone grafts with PRP at 1 and 2 months compared to autogenous bone alone. Discussion: In this study, growth factors, which were decreased in irradiated cortical and cancellous bone, showed increased expression at 1 and 2 months when PRP was added to autogenous bone grafts. Thus, PRP may have potential therapeutic applications when bone grafting is required in patients with reduced bone vascularity, including patients with previous head and neck irradiation, diabetes, and smoking habits. Conclusions: Decreased expression of PDGF, bFGF, and TGF-b was seen in radiated rabbit tibia as compared to nonirradiated controls, and increased expression of these growth factors was seen in PRP-containing autogenous bone grafts. (Basic Science) (More than 50 references) Keywords: animal study, bone grafting, cranial defects, growth factors, immunohistochemistry