 Idiopathic IBD includes Crohns disease CD and Ulcerative Colitis UC, which are chronic inflammatory disorders of the intestine. IBD is common in developed countries, with up to 1 in 200 of individuals affected by theses diseases. It is currently thought that the disease arises owing to a complex array of genetic, environmental and immunologic susceptibility factors. T cells are thought to cause the lesions, but the B cell population apparently has a significant role as well, through secreting antibodies against certain self-antigens. We believe that a major contribution to the understanding of the pathogenesis of IBD, and especially of the immune pathway leading to CD, can be achieved by analysis of the B cell clones participating in immune responses in the gut, in particular their immunoglobulin Ig variable region gene diversity, which has never before been studied in the context of IBD. 