As well as causing retention of biliary secretory products, bile duct obstruction is associated with other hepatic and systemic effects which are poorly understood. These latter changes contribute to the increased morbidity and mortality associated with surgery for biliary obstruction. This study examines the changes in liver blood flow occurring after common bile duct (CBD) ligation in the belief that relative hepatic ischaemia may contribute to dysfunction. A new method for measuring liver blood flow (LBF) based on the clearance of 133Xe from the liver following injection into the portal vein is described. With this new development, serial measurements of LBF can be performed in the conscious, unfasted rat. With the development of jaundice, a highly significant reduction in LBF is seen which is first evident 36 hours after CBD ligation. By the third day after ligation, LBF is only 54% of the control value. No fall in LBF is seen in rats subjected to sham ligation. The mechanism for the reduction in LBF is uncertain, but the delayed onset makes any relfex autonomic reaction unlikely.