Inflammatory joint diseases such as rheumatoid arthritis tend to destroy joint cartilage and bone matrices. Since bone resorption is a common characteristic of rheumatoid arthritis, one of the cell types thought to play a vital role in the destruction of these matrices are the osteoclasts. Osteoclasts and osteoclastogenic factors such as inflammatory cytokines and RANK-L are present within inflamed joints, and osteoclastic bone resorptive activities are also displayed, further suggesting the possibility that osteoclasts are responsible for the joint cartilage and bone matrix damage observed in this joint disease.