Approval of infliximab for treatment of Crohn's disease in late 1998 was a landmark event in medical therapy for inflammatory bowel disease. This agent was the first of many promised biologic response modifiers investigated in the last half decade, a result of progress in recombinant and monoclonal technologies and improvements in large-scale production of biologic agents. The notable efficacy of infliximab also sets a benchmark against which future biologic agents might be compared. Although it will be many years until active comparisons of these agents are made through clinical trials, sufficient clinical data is now available for critical appraisal of the potential and reality of these agents.