['Ursodeoxycholic acid (UDCA) therapy is associated with reduced risk of biliary pain and acute cholecystitis or pancreatitis in patients with cholesterol gallstones. The underlying mechanisms are understood incompletely, which prompted us to study the influence of UDCA treatment on composition, viscosity and sedimentable fractions of gallbladder bile in 25 patients with symptomatic cholesterol gallstones.', 'In two randomised groups, either UDCA (750 mg daily) or placebo was given to each patient 10-12 days before cholecystectomy. Gallbladder bile was collected intraoperatively and analysed for protein, mucin, lipid composition, cholesterol crystal observation time, amount of cholesterol in vesicles, viscosity and sedimentable fractions (cholesterol, protein, mucin, bilirubin).', 'UDCA-treated patients showed longer cholesterol crystal observation times and lower concentrations of total cholesterol and percentages of vesicular cholesterol in gallbladder bile. The concentrations of protein and mucin in gallbladder bile tended to be lower in the UDCA-treated group, but phospholipids, bile acids and bilirubin did not differ between the groups. Viscosity and the total sedimentable fractions of gallbladder bile decreased in the UDCA-treated patients.'] Does ursodeoxycholic acid decrease viscosity and sedimentable fractions of gallbladder bile in patients with cholesterol gallstones?