Abstract: The Applicant has discovered a cytokine profile that can accurately distinguish between ulcerative colitis (UC) and Crohn's disease (CD) in a subject having, or having symptoms of, inflammatory bowel disease (IBD). The profile of ulcerative colitis is increased IL-10 levels (compared with a reference IL-10 level, and decreased IL-23 levels (compared with a reference IL-23 level). The cytokine profile can be detected at a protein or genomic level, and is generally determined from a peripheral blood sample (i.e. a blood fraction such as serum, plasma, or blood cells such as peripheral blood mononuclear cells). Distinguishing between UC and CD in a subject with IBD allows a clinician prescribe a suitable therapeutic regime for the subject using a non-invasive blood test, and avoiding the need for scoping or tissue biopsy, which are undesirable for the subject. The cytokine profile can also be used to monitor a therapeutic regime for effectiveness.