Inflammatory bowel disease (IBD) is a generic term that refers to Crohn's disease and ulcerative colitis. Crohn's disease (CD) is a granulomatous enteritis which can involve the ileum, colon, and other parts of the intestinal tract. The serologic responses seen in Crohn's disease include antibodies to Saccharomyces cerevisiae, mycobacteria, bacteroides, listeria and E. coli. Many of these organisms may be involved in the pathogenesis of the Crohn's disease. Ulcerative colitis is characterized by inflammation of the mucosa and submucosa of the large intestine. The CD and UC are considered to be distinct forms of IBD; however, there is a subgroup of CD with a UC-like presentation. In recent years, several serologic markers have been found to be useful for the diagnosis and differentiation of CD and UC. These markers include the following antibodies (a) 2pANCA, (b) ASCA, (c) pancreatic antibody, and (d) OmpC antibody. The application of a panel of markers with the use of an algorithm can identify specific subtypes of IBD that have different clinical courses and progression of the diseases. The application of the serologic markers is useful for diagnosis and management of CD and UC patients.