Cytokines are low-molecular-weight protein mediators that possess a wide spectrum of inflammatory, metabolic, and immunomodulatory properties. Cytokines have been shown to be produced by monocytes/macrophages, lymphocytes, fibroblasts, endothelial cells, and more recently, hepatocytes and biliary epithelium. The aim of this study was to define biliary levels of interleukin-6 (IL-6) and tumor necrosis factor-alpha (TNF-alpha) in patients undergoing endoscopic retrograde cholangiopancreatography (ERCP) in various disease states. Fifty-four patients undergoing ERCP comprised the study group. IL-6 and TNF-alpha were measured in aspirated bile using an ELISA technique. Levels of both TNF-alpha and IL-6 were significantly higher in patients with cholangitis (P < 0.00001). Moreover, IL-6 was 100% specific for cholangitis since none of the patients without bacterial cholangitis-including patients with biliary obstruction secondary to cholangiocarcinoma or pancreatic carcinoma-had measurable IL-6 in their bile. Low levels of biliary TNF-alpha were detectable in five patients without cholangitis; the sensitivity and specificity of TNF-alpha for cholangitis were 100% and 82%, respectively. There was a strong statistical correlation between biliary IL-6 and TNF-alpha levels (r = 0.819, P < 0.0001). In contrast, the correlations between biliary cytokines and serum biochemical parameters were weak. These results suggest that IL-6 and TNF-alpha are sensitive markers for cholangitis and may differentiate it from other types of biliary tract disease.