The effects of low (control), moderate, and high biliary tract pressures on biliary lipid metabolism and bile flow were studied in six rhesus monkeys and two baboons. Moderate pressures did not influence bile flow or biliary lipid metabolism. High biliary tract pressures produced significant reductions in bile flow and the secretion rates of bile salts, phospholipids, and cholesterol, but cholesterol saturation in bile improved. High pressure also completely inhibited bile salt synthesis, and the bile salt pool size decreased slightly due to continuing small losses in urine and bile samples. During the high pressure period bile salts accumulated in the liver and peripheral tissues. After pressure had been returned to control levels, bile flow and biliary lipid secretion rates returned to normal levels. Bile salt secretion recovered more slowly than secretion of the other lipids and bile became more saturated with cholesterol than in the control period. Bile salt synthesis resumed approximately 10 hr after pressure had been returned to control levels. The high biliary tract pressures induced in these studies are no known to occur in about 25% of normal human subjects. (J Lab Clin Med 99:342, 1982.)