Today's issue of Science magazine has several articles on the human gut, the abstract of one of which appears below. I encourage you to read the articles and increase your knowledge in this important area. Science, Vol 307, Issue 5717, 1915-1920 , 25 March 2005 Host-Bacterial Mutualism in the Human Intestine Fredrik Beckhed, Ruth E. Ley, Justin L. Sonnenburg, Daniel A. Peterson, Jeffrey I. Gordon The distal human intestine represents an anaerobic bioreactor programmed with an enormous population of bacteria, dominated by relatively few divisions that are highly diverse at the strain/subspecies level. This microbiota and its collective genomes (microbiome) provide us with genetic and metabolic attributes we have not been required to evolve on our own, including the ability to harvest otherwise inaccessible nutrients. New studies are revealing how the gut microbiota has coevolved with us and how it manipulates and complements our biology in ways that are mutually beneficial. We are also starting to understand how certain keystone members of the microbiota operate to maintain the stability and functional adaptability of this microbial organ. Tom Billings