The assessment of disease activity in inflammatory bowel disease is done using clinical parameters and various biological disease markers. Classical disease markers including erythrocyte sedimentation rate, acute phase proteins, such as orosomucoid and CRP, leukocyte and platelet counts, play an important role in the monitoring of disease activity. Furthermore, the determination of zinc, iron, ferritin, vitamin B12, and folic acid is important to avoid deficiencies in patients with severe disease or after surgeries. Stool cultures are helpful to detect bacterial or parasitic infections mimicking inflammatory bowel disease. The detection of specific antibodies such as pANCA, PAB and ASCA is helpful for the differential diagnosis Crohn's disease--ulcerative colitis.