Abstract: To assess the diagnostic and prognostic value of interleukin-6, interleukin 1β, and tumor necrosis factor-α assays in plasma and ascites, we measured these cytokines in eight patients with malignancy-related ascites and 32 patients with decompensated cirrhosis. Five patients had an episode of bacterial peritonitis, during which one or more ascitic fluid samples were analyzed. Interleukin-6 and tumor necrosis factor-α were not significantly different between the cirrhotic and the malignant groups: ascitic interleukin-6 13 816±15 314 vs 28 138±23 403 pg/ml, plasma interleukin-6 542±719 vs 559±604 pg/ml; ascitic tumor necrosis factor-α 19±50 vs 12±31 pg/ml, plasma tumor necrosis factor-α 3.4±8.2 vs 6.1±13.8 pg/ml. During an episode of bacterial peritonitis there was a significant increase only in ascitic interleukin-6 (133 268±99 743 pg/ml), which declined after antibiotic treatment. None of the parameters was associated with 6-month survival (11 of the 40 patients died within 6 months). There was a correlation (r=0.675; p=0.002) between plasma interleukin-6 levels and the Child-Pugh score in patients with cirrhosis, but not with the etiology of the liver disorder. Plasma interleukin-6 levels correlated with IgA levels (r=0.649; p=0.004) but not with C reactive protein, sedimentation rate, fibrinogen, IgM or IgG. These results do suggest that interleukin-6 is produced within the peritoneal cavity in hepatic and malignant ascites. There is a sharp increase in the local production of interleukin-6 during an episode of bacterial peritonitis. This increase was not detectable for tumor necrosis factor-α. The physiological meaning of this over-production of locally generated cytokines and whether it relates to the poor prognosis of patients with cirrhosis and infectious disorders remain to be assessed.