Gallstone patients have a reduced total bile acid pool size. To analyze mechanisms behind this, the relation between gallbladder storage capacity and bile acid pool size was studied in 20 gallstone patients, 15 women and 5 men. At cholecystectomy bile was aspirated from the gallbladders, and the volume of bile and concentration of bile acids were recorded. The total bile acid pool size was at the same time estimated by an isotope dilution technique. A significant positive correlation between gallbladder volume and bile acid pool size was found (r = 0.45). The correlation between bile acid concentration in the gallbladders and pool size was, however, not significant (r = 0.24). It is suggested that gallbladder storage capacity may be a determinant of bile acid pool and that a diminished pool size, as seen in gallstone disease, may to some extent be caused by gallbladder fibrosis and shrinkage.