1. The human gall bladder acidifies the bile. In this respect its action is similar to that of the gall bladders of lower animals, previously described by other workers.
2. The hydrogen ion concentration of gall bladder bile is increased considerably in cases of obstruction of the common or cystic ducts. The highest values were found following complete obstruction.
3. The occurrence of gall stones was not associated with a consistent change in the hydrogen ion concentration of the gall bladder bile.