An analysis of bile composition following orthotopic liver transplantation in the rhesus monkey showed that during rejection only small quantities of viscid bile were produced and that this was associated with increased cholesterol saturation. Bile composition in patients after liver transplantation also showed that bile was supersaturated with cholesterol in the early postoperative period while the enterohepatic circulation of bile acids was interrupted by a draining T tube. However, further study of patients showed a poor correlation between bile composition and the development of biliary complications. An analysis of bile 'sludge' showed that after transplantation two types were encountered. The first, containing large quantities of unconjugated bilirubin, was present when intrabiliary obstruction was associated with long-standing mechanical obstruction. The second type, present in patients developing masses of intrabiliary 'sludging' shortly after transplantation, consisted mainly of necrotic donor biliary tract due to damage during preservation. An intrabiliary perfusion technique was developed which in animal models reduced the extent of donor biliary damage.