This thesis is based on the following papers, referred to in the text by their roman numerals: I Erichsen K, Hausken T, Ulvik RJ, Svardal A, Berstad A, Berge RK. Ferrous fumarate deteriorated plasma antioxidant status in patients with Crohn disease. Scand J Gastroenterol 2003;38:543-548. - II Erichsen K, Milde AM, Arslan G, Helgeland L, Gudbrandsen OA, Ulvik RJ, Berge RK, Hausken T, Berstad A. Low-dose oral ferrous fumarate aggravated intestinal inflammation in rats with DSS-induced colitis. Inflamm Bowel Dis 2005;11:744-748. - III Erichsen K, Ulvik RJ, Nysaeter G, Johansen J, Ostborg J, Berstad A, Berge RK, Hausken T. Oral ferrous fumarate or intravenous iron sucrose for patients with inflammatory bowel disease. Scand J Gastroenterol 2005;40:1058-1065. - IV Erichsen K, Ulvik RJ, Grimstad T, Berge RK, Berstad A, Hausken T. Effects of ferrous sulphate and non-ionic iron-polymaltose complex on markers of oxidative tissue damage in patients with inflammatory bowel disease. Aliment Pharmacol Ther 2005;22:831-838.