Crohn's disease and ulcerative colitis known as inflammatory bowel diseases, are chronic inflammatory disorders involving the gastrointestinal tract. Because the cause of both disease remains unknown, a curative therapy has been lacking. Until recently, conventional treatments have focused on nonspecific suppression of the inflammatory process and are often effective in achieving symptomatic control, but frequently fail to prevent relapse when administered over time. Recent advances in basic research have provided new insights into the role of specific immune cells and their mediators in intestinal inflammation. Such understanding has led to the development of biologic treatments directed at altering specific pathogenic mechanisms that have the potential to modifiy the natural course of these disorders. The compounds directed against important regulatory cytokines such as tumor necrosis factor-alpha ( TNF-α ) have demonstrated the greatest clinical efficacy to date. These clinical findings are consistent with scientific observations that have suggested a central role of TNF-α in chronic intestinal inflammation. It is probable that biologic therapy will play an important role in the future treatment of inflammatory bowel diseases. ( Korean J Gastroenterol 2002; 40: 219-227)