The aim of the present study was to demonstrate the mitogenic and differentiating properties of platelet-rich plasma releasates (PRPr) on human chondrocytes in mono- and three-dimensional cultures. In order to assess if PRPr supplementation could maintain the chondrocyte phenotype or at least inhibit the cell de-differentiation even after several days in culture, we performed a proteomic study on several cell cultures independently grown, for different periods of time, in culture medium with FCS, human serum (HS), and releasates obtained from PRP and platelet-poor plasma (PPP). We found that PRP treatment actually induced in chondrocytes the expression of proteins (some of which novel) involved in differentiation.