Studies have shown that this so-called "gut microflora" can influence the immune system, how the body responds to foods, the action of drugs, and other functions. Researchers started the new study after noting that a genetically identical population of rats widely used in laboratory tests had developed two distinctively different metabolic types. The types involve differences in the way those animals metabolize, or breakdown, drugs and nutrients. The research article, entitled "Metabonomic Evaluation of Schaedler Altered Microflora Rats" is scheduled for the Dec. 7 issue of ACS' Chemical Research in Toxicology.