Immunosuppressive (IS) drugs are an important option in the management of both forms of inflammatory bowel disease (IBD): Crohn's disease and ulcerative colitis. As the experience of using these agents in the treatment of IBD has increased and more data have become available on their efficacy, these drugs are being used more extensively. The principle drugs used in clinical practice at this time include: azathioprine (AZA) and its metabolite 6-mercaptopurine (6-MP), methotrexate, and cyclosporin A. AZA and 6-MP are generally considered the first line immunosuppressive agents. These drugs are effective and generally well tolerated by the majority of patients started on them, enabling many patients to avoid the predictable side effects of steroid therapy. Because of their extensive use, it is important that clinicians involved in the care of IBD patients are familiar with the IS drugs used to treat IBD, especially AZA and 6-MP.