Isotopic bile salt studies were carried out in eight middle-aged women with radiolucent galstones in functioning gallbladders and in 10 matched controls. In the gallstone patients the size of the bile salt pool was reduced by 37% to 1.79 g, but there was considerable overlap with the normal subjects. The cholate and chenodeoxycholate pools were reduced, but the deoxycholate pool was normal in size. There were changes in bile salt metabolism which resembled those found after cholecystectomy but were less marked. This suggests that in gallstone disease the storage capacity of the gallbladder is impaired. This may contribute to the small bile salt pool, but it is unlikely to be the sole or even the major cause.