In rheumatoid arthritis and inflammatory bowel disease, such as Crohn's disease, certain immunological abnormalities are considered as its cause, but the fundamental mechanism remains unclear. However, recent researches revealed that inflammatory cytokines, such as TNF-alpha, IL-1 and IL-6, are greatly involved in these immunological abnormalities. This led to the development of anti-cytokine therapy using monoclonal antibodies to these cytokines. Among them, Infliximab, a chimeric monoclonal antibodies to TNF-alpha, is most clinically applied and marked therapeutic effect is seen in various diseases.