Biomarkers predictive of responsiveness to integrin beta7 antagonists, including anti-beta7 integrin subunit antibodies, and methods of using such biomarkers are provided. In addition, methods of treating gastrointestinal inflammatory disorders such as inflammatory bowel diseases including ulcerative colitis and Crohn' s disease are provided. Also provided are methods of using such predictive biomarkers for the treatment of inflammatory bowel diseases including ulcerative colitis and Crohn' s disease.