To study the effects of oxidative stress on the intestinal tract, Caco-2 cells were treated with a 75 micromolar hydrogen peroxide (H 2O2) solution for 30 minutes. After RNA isolation and purification, analysis of gene expression was obtained via microarrays. Gene expression levels were confirmed by RT-PCR. Results indicate no expression changes in the antioxidant enzymes, catalase, superoxide dismutase, glutathione peroxidase, and glutathione reductase, which could be explained by their high kcat /Km ratios indicative of high catalytic efficiency. Gene expression of the cytochrome P450 enzyme CYP2B6 was upregulated 32%, which could indicate an important role for it in prevention or exacerbation of oxidative damage. CYP2B6 is one of approximately 60 CYP450 enzymes in humans responsible for the biotransformation of xenobiotics and endogenous organic compounds. Results indicated a repression in genes involved in lipid and cell membrane synthesis, such as fatty acid desaturase 2. Insulin-like growth factor 2 and S-phase kinase-associated protein 2, two genes involved in cell cycle progression and cell growth were down-regulated as well. Results indicated a repression in the transcriptional genes, Sp1 transcription factor and MYC-associated zinc finger protein. Also, DEAD box polypeptide 21 and DEAH box polypeptide 9, genes involved in RNA processing, were down-regulated. Other genes involved in translation, angiogenesis, DNA repair, protein processing, glucose production, cell to cell adhesion, and cell signaling were repressed as well. Results indicate that H2O2 inhibits the growth and proliferation of Caco-2 cells. This inhibition of Caco-2 cell proliferation and the induction of CYP2B6 may be novel key regulatory factors involved in protecting or damaging the intestine from oxidative stress.