Patients hospitalized with severe ulcerative colitis can least afford suboptimal infliximab therapy, but are at highest risk given their malnutrition and uncontrolled inflammation. There is a growing trend towards the use of high dose of infliximab as the first line therapy in these severe, hospitalized patients as they have just one infusion (dose) to demonstrate clinical response before they are referred for colectomy. However, there is currently no pharmacokinetic data to support this practice. There is only a small body of literature that serum infliximab trough levels may predict clinical outcomes in acute ulcerative colitis. To our knowledge, there are no studies regarding the use of early infliximab levels - within the first 72 hours - to predict clinical response in the vulnerable subset of patients hospitalized for severe ulcerative colitis.