AIM An increased viscosity of gallbladder bile has been considered an important factor in the pathogenesis of gallstone disease. Besides lipids and proteins, mucin has been suggested to affect the viscosity of bile. To further clarify these issues we compared mucin, protein and the lipid components of hepatic and gallbladder bile and its viscosity in patients with gallstones.METHODS Viscosity of bile (mPa. s) was measured using rotation viscosimetry in regard to the non-Newtonian property of bile at lowshear rates.RESULTS Biliary viscosity was markedly higher in gallbladder bile of patients with cholesterol (5.00±0.60 mPa.s, mean±SEM, n-28) and mixed stones (3.50±0.68 mPa.s; n =8) compared to hepatic bile (0.92±0.06 mPa.s,n =6). A positive correlation between mucin andviscosity was found in gallbladder biles (r =0.65; P<0.001) but not in hepatic biles. The addition of physiologic and supraphysiologic amounts of mucin to gallbladder bile resulted in a dose dependent non linear increase of its viscosity. A positive correlation was determinedbetween phospholipid concentration and viscosity (r = 0.34, P<0.005) in gallbladder biles. However, no correlation was found between total protein or the other lipid concentrations and viscosity in both gallbladder and hepatic biles.CONCLUSION The viscosity of gallbladder bile is markedly higher than that of hepatic bile in patients with gallstones. The concentration of mucin is the major determinant of biliary viscosity and may contribute by this mechanism to the role of mucin in the pathogenesis of gallstones. AIM An increased viscosity of gallbladder bile has been considered an important factor in the pathogenesis of gallstone disease. To lipids and proteins, mucin has been suggested to affect the viscosity of bile. To further clarify these issues we compared mucin, protein and the lipid components of hepatic and gallbladder bile and its viscosity in patients with gallstones. METHODS Viscosity of bile (mPa. s) was measured using rotation viscosimetry in regard to the non-Newtonian property of bile at lowshear rates. RESULTS Biliary viscosity was markedly higher in gallbladder bile (5.00 ± 0.60 mPa.s, mean ± SEM, n-28) and mixed stones (3.50 ± 0.68 mPa.s; n = 8) compared to hepatic bile (0.92 ± 0.06 mPa.s, n = 6 ) A positive correlation between mucin and viscosity was found in gallbladder biles (r = 0.65; P <0.001) but not in hepatic biles. The addition of physiologic and supraphysiologic amounts of mucin to gallbladder bile resulted in a dose dependent non linear incrementation A positive correlation was determined between phospholipid concentration and viscosity (r = 0.34, P <0.005) in gallbladder biles. However, no correlation was found between total protein or the other lipid concentrations and viscosity in both gallbladder and hepatic biles. CONCLUSION The viscosity of gallbladder bile is markedly higher than that of hepatic bile in patients with gallstones. The concentration of mucin is the major determinant of biliary viscosity and may contribute by this mechanism to the role of mucin in the pathogenesis of gallstones.