Abstract: Using RNA samples from mononuclear blood cells, gene sequences were identified that can be used to identify patients with IBD, and then distinguish patients with Crohn's disease from those with ulcerative colitis. Sequences were identified whose overexpression was distinct to patients with IBD, Crohn's disease, and ulcerative colitis when compared to patients with non-IBD intestinal disorders. Additionally, cluster analysis was used to identify twenty-five sequences that are IBD-related, and whose transcription pattern can be used in a microarray analysis to identify patients with IBD with a sensitivity of 84% and a specificity of 100%. Cluster analysis also identified thirty-six genes that could be used to distinguish patients with Crohn's disease from those with ulcerative colitis with a sensitivity of 89% and a specificity of 80%.