Abstract In gallbladder and common duct bile from patients undergoing cholecystectomy, usually because of gallstones, calcium was found to exist in at least 2 forms. Ultrafiltration showed some calcium was bound to substances with a molecular weight greater than 10 000, and the chief binding agent is likely to be the mixed micelle. Bound calcium was significantly less in common duct bile than in bile from functioning gallbladders, but the amount of ultrafiltrable calcium was the same. Furthermore, ultrafiltrable calcium in gallbladder bile from patients with cholesterol or some calcium carbonate in their gallstones was almost constant for a range of total calcium concentrations of 2.40–9.70 mmol/l. Comparison of ultrafiltrable and total calcium values for the different types of stone-formers showed that the deposition of calcium carbonate in gallstones was not related to any calcium measurement made. However, the presence of calcium phosphate and/or calcium bilirubinate in gallstones could be related to a significant increase in ultrafiltrable calcium in gallbladder bile.