Infliximab reduces the effects of a substance in the body that can cause inflammation. Infliximab is used to treat rheumatoid arthritis, psoriatic arthritis, ulcerative colitis, Crohn's disease, and ankylosing spondylitis. Infliximab is also used to treat severe or disabling plaque psoriasis (raised, silvery flaking of the skin). Infliximab is often used when other medicines have not been effective. Infliximab may also be used for purposes not listed in this medication guide.