The effect on biliary lipid and bile acid composition was assessed during the development of gallbladder nonfunction in 5 subjects with asymptomatic cholesterol cholelithiasis. There was a significant increase in the relative proportion of bile salt but a decrease in that of cholesterol in bile after development of gallbladder nonfunction which persisted after recovery from cholecystectomy. These findings were associated with a decrease in cholesterol crystals in bile sediment and an increase in the proportion of secondary bile acids after cholangiographic evidence of gallbladder nonfunction. Percentage cholesterol saturation of bile reverted to normal after development of gallbladder nonfunction which persisted after recovery from cholecystectomy.