I can't tell how old this article from UNC is, but I thought it was interesting:Hormones and IBS In particular:"Our research group has conducted two small studies which indicate that another gut hormone, vasoactive intestinal peptide (VIP), is abnormally concentrated in IBS patients. In the first study(16), we measured the concentration of several substances in samples of the mucosal lining of the rectum, looking for evidence of possible low-grade inflammation of the bowel. We found no evidence of inflammation, but we noted that the gut hormone VIP was twice as concentrated in the samples from 16 IBS patients compared to the 17 control subjects. This difference was statistically significant..." The second study had similar findings, the authors say. Being no great fan of the Rome criteria, I'm hoping they might be on to something diagnostically there...