Pleiotrophin or osteoblast-specific factor 1(HOSF-1) is a growth-associated protein present in bone matrix. This study was designed to study pleiotrophin expression in osteoblastic cells. Pleiotrophin was expressed by osteoblast-like cell line. Pleiotrophin expression increased following the proliferative phase and was minimal at the terminal phases of the induced differentiation of cultured MC3T3-E1 cells. Pleiotrophin expression represents another autocrine factor that may contribute to the physiologic control of induced bone formation. In this study, induced osteogenesis will be examined in the context of the osteoblast expression of and regulation by PTN. I hypothesized that PDGF-BB stimulation of PTN expression represents an important paracrine signal during the induced osteogenesis associated with periodontal and implant surgeries. The possible mediation by PTN of anabolic effects attributed to PDGF-BB stimulation was examined in cell culture models of osteoblast differentiation. These studies will contribute fundamental insights to osteoblast biology and insights regarding the potential use of factors such as PTN in the clinical environment.