The present study assessed whether peritoneal macrophages isolated from cirrhotic patients produce nitric oxide (NO) and express NO synthase type II (NOS II) mRNA and protein. Patients with cirrhosis and ascites without peritonitis or with unresolved or resolved spontaneous bacterial peritonitis (SBP) were studied. Following paracentesis, ascites NO + NO content (NOx) was measured. Peritoneal macrophages from ascites were seeded on well plates, and NO in the medium was determined. NOx was higher in patients with unresolved or resolved SBP than in cirrhotic patients without peritonitis. Macrophages of patients with SBP or resolved SBP produced NO after 30 hours in culture, but those obtained from patients without peritonitis did not. Reverse-transcription polymerase chain reaction (RT-PCR) and immunocytochemical analysis revealed the presence of a clear signal for NOS II mRNA and protein in macrophages of SBP patients, regardless of whether or not the infection subsided. Therefore, peritoneal macrophages isolated from cirrhotic patients with unresolved or resolved SBP produce NO and express the NOS II mRNA and protein, suggesting that NOS II may contribute to the control of SBP, or to its associated pathology, in human cirrhosis.