New therapies, in particular the tumor necrosis factor-alpha-blocking drugs, have led to improved control of inflammation in rheumatoid arthritis for a proportion of patients. There remains a need for therapies for patients who do not respond to these drugs or in whom they are contraindicated or not tolerated. There is evidence that T cells are involved in the initiation and perpetuation of rheumatoid arthritis. Abatacept is the first in a new class of drugs targeted at T-cell function in autoimmune disease: the costimulation blockers. It has shown safety and efficacy in rheumatoid arthritis. Further trials of this and other costimulation blockers are in progress in rheumatoid arthritis and other diseases.