This review in depth considers the thiopurines azathioprine, 6-mercaptopurine and 6-thioguanine, methotrexate, ciclosporin, infliximab and less well-established immunomodulators (including thalidomide, mycophenolate, tacrolimus and natalizumab among others) in their role of modifying the course of ulcerative colitis and Crohn's disease. The five papers are preceded by an overview on the therapeutic order of precedence, the indications and duration of therapy, as well as future concepts.