The role of immunosuppressives in the treatment of Crohn's disease and ulcerative colitis will be reviewed. This will include a comprehensive presentation of the uncontrolled and controlled studies in both diseases. The author's personal experiences with more than 400 patients will be summarized, including efficacy and short- and long-term toxicity. A review of the literature regarding the risk of superinfections and neoplasia will be presented. Finally, specific indications for the use of 6-MP/azathioprine will be listed.