Whole tissues corresponding to the proximal and distal small intestine and to the colon were dissected from each rat, washed with ice-cold saline solution and immediately frozen in liquid nitrogen. Rats were either control or treated with Amoxicillin (100mg/kg/day). Small intestine was divided in two identical length considered as the proximal and distal part. In each intestinal part 1 cm of tissue was taken in the middle of this part to perform the RNA extraction and then the GeneArray analysis. Keywords = gastrointestinal tract, microarray, antibiotic, suckling rats, amoxicillin