Purpose: To evaluate the effect of the addition of platelet concentrate (PC) to autografts or bone substitutes on bone regeneration in standardized bone defects. Materials and Methods: Three standardized bone defects were prepared in both mandibular angles of 12 adult minipigs. The defects were grafted with autograft, anorganic bovine bone, or synthetic b-tricalcium phosphate (b-TCP). PC was added to only 1 side. The animals were divided into 4 groups, which were sacrificed at 4 different time points (1, 2, 4, and 8 weeks) for histologic and histomorphometric analysis. The concentrations of platelets and growth factors were measured to identify correlation to the histologic and histomorphometric results. Results: No correlation was found between platelet count in whole blood and platelet count in PC (rp = 0.36). Furthermore, no correlation could be demonstrated between the platelet count of the PC and the concentrations of PDGF-AB (rp = -0.27) and TGF-b (rp = 0.34). There were no signs of a stimulating effect of PC on bone formation in combination with autografts or bone substitutes at any time point (P = .89). Addition of PC did not alter the pattern of graft degradation. Discussion: The present study underlines the need for further investigation to identify the optimal concentrations of platelets and combinations of growth factors to achieve a predictable stimulatory effect on bone regeneration. One of the first steps to achieve this goal will be the development of a reliable method for the procurement of PC. Conclusion: PC had no impact on bone formation and graft degradation in standardized bone defects in the mandibles of minipigs. Keywords: autogenous bone grafting, bone regeneration, bone substitutes, growth factors, platelet concentrates, platelet-rich plasma