Background and Aims. Necrotizing enterocolitis (NEC) is a disease of neonates that is increasing in incidence and often results in significant morbidity and mortality. Carbon monoxide (CO), a byproduct of the catabolism of heme, is known to have anti-inflammatory and anti-apoptotic properties. The purpose of these experiments is to demonstrate that inhaled CO protects against the development of intestinal inflammation in a model of experimental NEC as well as decreases enterocyte cell death in vitro. Additionally, that CO decreases enterocyte production of inducible nitric oxide synthase (iNOS) and nitric oxide (NO). Methods. Neonatal rats were exposed to intermittent hypoxia exposure and formula-feeding to induce experimental NEC. Animals randomized to CO treatment were put in an environment containing 0.025% CO for one hour per day on days of life one to three. All animals were sacrificed on day of life four. In vitro experiments were performed using IEC-6 cells, a rat enterocyte cell line. Cells were examined for viability, iNOS production and elaboration of NO. Results. CO diminished levels of serum inflammatory cytokines and nitrites, protected against intestinal inflammation, and decreased ileal iNOS production and protein nitration in a model of experimental NEC. In vitro, CO decreased cytokine- or hypoxia/endotoxin-induced iNOS/NO production. Additionally, CO abrogated tumor necrosis factor-/actinomycinD-induced apoptosis or hypoxia/endotoxin-induced cell death. Conclusions. One-hour daily of low dose inhaled CO protected against the development of intestinal inflammation in a model of experimental NEC. iNOS and NO production were decreased by CO both in vivo and in vitro. CO may prove to be a useful clinical adjunct in the treatment of NEC.