During the decade in which the medical dissolution of gall stones has become feasible several drugs have been introduced but only the two listed in the British National Formulary have been intensively evaluated and shown to be effective--chenodeoxycholic acid and the closely allied ursodeoxycholic acid. The dissolution of gall stones was last reviewed in the "BMF" in 1976, at which stage experience with chenodeoxycholic acid was limited. Since then the indications and potential for this bile acid in treating gall stones have become better understood, and data on the newly introduced ursodeoxycholic acid are being evaluated. Cholesterol, but not pigment, gall stones are amenable to oral dissolution treatment. This review will cover firstly, chenodeoxycholic acid, secondly, ursodeoxycholic acid, then a comparison of the two drugs, an assessment of the place of medical dissolution in the management of gall stones, and, finally, the dissolution of stones in the common bile duct.