Recent studies demonstrate the ability of IL-1 and TNF-® to induce both osteoclast formation and bone-resorbing activity (64–66). These studies suggest that activated macrophages may facilitate bone resorption by participating in osteoclast formation and activation.The role of TNF-® in regulating osteoclastic bone resorption continues to be elucidated with studies demonstrating that osteoblasts/stromal cells express a new member of the TNF-ligand family—osteoclast differentiation factor (ODF)/osteoprotegerin (OPGL)/TNF-related activation-induced cytokine (TRANCE)/receptor activation of NF-·B ligand (RANKL)—as a membrane associated factor (66–68).