Isoprostanes are compounds that are produced as a result of oxidative damage to cell membranes. Elevated tissue, serum, and urinary isoprostane levels have been described in a number of inflammatory diseases. The goal of this study is to determine utility of measuring urinary isoprostane levels in pediatric patients with inflammatory and non-inflammatory gastrointestinal disease. Urine samples will be collected from pediatric patients undergoing procedures in the Children’s Hospital endoscopy unit. Clinical disease activity will be assessed using a standardized clinical disease activityiIndex. Gross endoscopic and histologic findings will be graded. Previously obtained laboratory studies will also be recorded. Urinary Isoprostane levels will be determined using a commercially available assay. Isoprostane levels will be compared across conditions (IBD vs. non-inflammatory, Crohn’s disease vs. ulcerative colitis) and tested for statistical significance. Similarly, disease severity and urinary isoprostane levels will be assessed. The sensitivity, specificity, and positive and negative predictive values of elevated urinary isoprostane levels at discriminating pediatric patients with inflammatory and non-inflammatory gastrointestinal disease will be calculated.