This protocol will examine blood, synovial fluid and synovial tissue from patients with rheumatoid arthritis and other chronic inflammatory joint diseases to study genetic and immunologic factors involved in the cause, development and progression of these conditions. Synovial fluid is the lubricating fluid in joints. The synovial membrane is a delicate tissue lining the inner surface of joints, which, in arthritic conditions, thickens and becomes infiltrated with various types of cells.

Patients with rheumatoid arthritis and certain patients with other forms of arthritis may be eligible for this study. Those enrolled will be followed periodically for follow-up and disease evaluation. They may undergo the following procedures:

1. Synovial fluid aspiration, when medically indicated (for example, for joint swelling and inflammation). For this procedure, an area of skin around the joint is numbed with an anesthetic, and a needle is inserted into the joint to withdraw a small fluid sample.
2. Periodic blood sampling, not to exceed 450 milliliters (15 ounces) during any 6-week period, for genetic studies of rheumatoid arthritis. The samples are usually taken at the same times that synovial fluid is withdrawn.
3. Synovial tissues, collected by needle biopsy or during surgical procedures for arthroscopy (examination of the interior of the joint and repair of the joint) or total joint replacement. For the needle biopsy, the skin over the biopsy site is washed and anesthetized. A needle is inserted and fluid is aspirated. The biopsy needle is then inserted through the outer needle and a tissue sample is suctioned.

Patients who qualify for other research studies may be invited to participate.