BACKGROUND: Osteoprotegerin(OPG) is a soluble member of the tumor necrosis factor(TNF) receptor family and inhibits osteoclastogenesis by interrupting the cell-to-cell interaction between osteoblastic/stromal cells and osteoclast progenitors. OPG is expressed in many tissues including osteoblasts and may act on bone tissues in a paracrine and/or autocrine fashion. Futhermore, many cytokines and growth factors are known to influence the regulation of OPG expression in osteoblastic/stromal cells. The aims of the present study were to examine whether or not OPG was expressed in human peripheral blood mononuclear cells(PBMCs) and to investigate the effects of IL-1beta, which were known as potent osteotropic agents, on the regulation of OPG mRNA in PBMCs. METHODS: PBMCs were isolated by centrifugation over Ficoll-Hypaque density gradients from postmenopausal women and cultured in 6-well plates containing alpha-MEM supplemented with 5% FBS. The expression of OPG mRNA in PBMCs was observed by RT-PCR in adherent and nonadherent cells on culture plates. To observe the effect of OPG expression by IL-1beta, we measured the concentration of OPG mRNA by altering the concentration and incubation time of IL-1beta. The measurement of OPG mRNA was done by semi-quantitative PCR and indicated as OPG/GAPDH. RESULTS: OPG was expressed both in cells attached to the surface of culture plates and in non-adherent cells for the incubation of peripheral blood mononuclear cells. The effect of OPG mRNA by IL-1beta tend to increase in accordance with the length of incubation time and maximizes at 12 hours of incubation time and shows 1.2-3.5 times higher than the standard level at the concentration of 0.5ng/ml. However, the increased quantity in concentration varies according to individuals.] CONCLUSION: OPG mRNA is expressed in peripheral blood mononuclear cells and known to be increased by IL-1beta.