Abstract: The present invention relates to the use of components of the IL23 pathway as biomarkers, e.g., IL22, LCN2 and combinations thereof, to stratify or identify populations of patients suffering from IL23-mediated diseases (e.g., Crohn's disease) responsive to treatment with an anti-IL23 antagonist (including, e.g., anti-IL23 antibodies or antigen-binding fragments thereof). Levels of IL23 pathway biomarkers above or below a predetermined threshold can be used, for example, (i) to determine whether a patient with an IL23-mediated disease or disorder such a Crohn's disease is eligible or non-eligible for treatment with a therapeutic agent (e.g., an ant-IL23 antibody), (ii) to determine whether treatment with a certain agent should be commenced, suspended, or modified, (iii) to diagnose whether the IL23-mediated disease is treatable or not treatable with a specific therapeutic agent, or (iv) to predict the outcome of treating the IL23-mediated disease with a specific therapeutic agent.