Background: Ammonia plays a major role in the pathogenesis of hepatic encephalopathy however oxidative stress is also believed to be involved. Two lines of evidence lead us to the following aim of our study: 1) neurotoxic levels of ammonia have demonstrated to induce oxidative stress in vitro and 2) systemic oxidative stress is believed to exacerbate the neuropsychological effects of hyperammonemia observed in patients with liver disease. Our aim was to measure oxidative stress markers systemically and centrally, in association with brain edema in rats with cirrhosis. Methods: Rats were sacrificed 6 weeks following bile-ligated induced cirrhosis. Arterial plasma and cerebrospinal fluid (CSF) were collected to measure ammonia (commercially available kit), reactive oxygen species (ROS) (DCFDA-fluorescent technique), nitric oxide (NO) (Griess method) and lipid peroxidation (malondialdehyde, MDA) (commercially available kit). Frontal cortex was dissected to measure antioxidant catalase activity (Amplex Red fluorescent technique), S-nitrosylation of cystein thiols (immunoblotting) and brain water content was determined using the specific gravimetric technique. Results: Brain water content increased in BDL rats vs SHAM-operated controls (81.91 ± 0.19% vs 81.23 ± 0.20%, p<0.05). BDL rats vs SHAM-operated controls developed an increase in plasma arterial levels of ammonia (91.8 ± 18.4uM vs 41.2 ± 13.2uM, p<0.05), ROS (4.9 fold increase), NO (2.9 fold increase), MDA (41.9 ± 7.4uM vs 9.9 ± 0.6uM, p<0.005), S-nitrosylated proteins and a decrease in catalase activity (1.3 ± 0.5U/ml vs 3.2 ± 1.4U/ml, p<0.05). Centrally, BDL rats vs SHAM-operated controls developed an increase in CSF ammonia (123.5 ± 21.7uM vs 23.3 ± 6.1uM, p<0.05) but did not develop an increase in CSF ROS and NO or in brain MDA and S-nitrosylation detection. Furthermore, catalase activity in the brain was unchanged in BDL vs SHAM-operated controls. Conclusions: Six weeks following BDL, rats developed brain edema. An increase in arterial ammonia was accompanied with an increase in lipid peroxidation, NO, ROS and S-nitrosylation with a decrease in catalase activity. However, a similar increase in ammonia levels in CSF lead to contrary results where no increase in oxidative stress markers was found in brain. Our findings suggest 1) ammonia does not induce oxidative stress in the brain, 2) systemic oxidative stress is related to a decrease in catalase activity and 3) brain edema in BDL rats is associated with systemic, and not central, oxidative stress.