In aging societies, osteoporosis and other age-related bone metabolism disorders are a rapidly increasing problem. The amount of bone in an organism is controlled by a balance of osteoblasts (bone-forming cell) and osteoclasts (bone-destroying cell) activities. A method to induce osteoclasts formation from bone marrow cells using M-CSF (macrophage-colony stimulating factor) and RANKL (receptor activator of NF-?B ligand) has been established in recent years. This kit includes cryopreserved primary precursor osteoclasts from mouse bone marrow and Culture Medium containing M-CSF and RANKL.