Natalizumab is a humanized, monoclonal antibody, that inhibits adhesion molecules (alpha(4)-integrins) on the surface of immune cells. These adhesion molecules are important for binding of lymphocytes to endothelial cells of blood vessels and infiltration of inflammatory cells into tissues. Natalizumab is currently being tested in large clinical trials for the treatment of multiple sclerosis (MS) and other autoimmune diseases (inflammatory bowel diseases, rheumatoid arthritis). After demonstrating the safety and potential effectiveness of natalizumab in MS therapy during shorter treatment periods (