The expression of the colonic mitochondrial 3-hydroxy 3-methyl glutaryl CoA (mHMGCoA) synthase,a key con-trol site of ketogenesis from butyrate,is lower in germ-free (GF) than in conventional (CV) rats. In contrast,the activity of glutaminase is higher. The objective of this study was to investigate whether the intestinal flora can affect gene expression through short chain fatty acid (SCFA) and butyrate production. GF rats were inoculated with a con-ventional flora (Ino-CV) orwitha bacterial strainproducing butyrate (Clostridium paraputrificum,Ino-Cp) or not (Bifidobacterium breve,Ino-Bb). .