['Spontaneous bacterial peritonitis (SBP) is a major complication of liver cirrhosis and accounts for significant mortality. Although oxygen free radicals and nitric oxide been implicated in the pathophysiology of liver cirrhosis, information on their role during the development of SBP is scarce. This study examined these active species in ascitic fluid from patients with SBP, and in response to treatment.', 'Forty-nine consecutive patients with cirrhosis and ascitic fluid neutrophil counts less than 250/cumm were studied as controls. Another 21 patients whose ascitic neutrophil count exceeded 250/cumm were treated as cases. Ascitic fluid was collected from these patients at entry and 48 h after treatment with antibiotics. Nitrate and markers of oxidative stress such as malondialdehyde, protein carbonyl content and total and protein thiols were measured.', 'A significant increase in malondialdehyde and protein carbonyl levels was seen in ascites from patients with SBP when compared to controls. This was accompanied by a decrease in total thiols and protein thiols. In addition, there was a significant increase in ascitic fluid nitrate in patients with SBP when compared to control patients. After antibiotic treatment, malondialdehyde, protein carbonyl and nitrate levels dropped back towards control values, and total thiols also recovered.'] Does spontaneous bacterial peritonitis result in oxidative and nitrosative stress in ascitic fluid?