Tumor necrosis factor–alpha (TNF,α), a cytokine that is produced in a variety of inflammatory diseases associated with cholestasis, is believed to be the primary mediator of the systemic effects of endotoxin. Thus, we have investigated the role of TNFα in the pathogenesis of endotoxin-induced cholestasis in intact animals, and in the uptake of taurocholate by cultured hepatocytes. Male Sprague-Dawley rats received either intravenous (IV) endotoxin (7.5 mg/kg) or monoclonal anti-TNFα antibody followed by endotoxin. Basal bile flow and bile salt excretion were measured for a 2-hour period, after which all animals received an IV bolus of taurocholate (10 μmol/100 g body weight). Endotoxin decreased basal bile flow by 41% and bile salt stimulated bile flow by 38% (n = 12; P < .01). Basal bile salt excretion was decreased 86% after endotoxin administration. Passive immunization with anti-TNFα antibody blocked this endotoxin-associated cholestasis. In addition, rat hepatocytes were isolated and cultured in the presence of either endotoxin (10 μg/mL) or TNFα (100 ng/mL) for 24 hours. These primary hepatocyte cultures exhibited a dose- and timedependent, noncompetitive, inhibition of taurocholate uptake. We postulate that TNFα is an important mediator of the cholestasis of sepsis. (HEPATOLOGY 1995; 22:1273–1278.).