Three enzyme immunoassays are available for the measurement of human Osteoprotegerin (OPG), free sRANKL, and free sRANKL in rat/mouse samples. Both OPG and sRANKL are markers that can be used to monitor the processes involved in bone metabolism. Via their respective pathways, they are both indirect regulators of osteoblast and osteoclast production, as a result of which they may be useful in indicating imbalances in bone formation and readsorption. The assays are research tools for investigational studies in osteoporosis, Paget’s disease, prostate and breast cancers, bone metastases, multiple myeloma, cardiovascular disease, pharmaceutical research and drug discovery and development affecting bone. Free sRANKL could also be used for studies in immunological and inflammatory disorders. The assays can be used for serum, plasma and cell culture specimen types. The kits are available in a 96-well format. ELISA methodology offers long shelf life and eliminates the use of radioactive reagents.