Methyl tert-butyl ether is an effective dissolution agent for cholesterol stones. The aim of this work was to evaluate the effect of methyl tert-butyl ether on radiolucent common bile duct stones in patients in whom endoscopic extraction has failed. From September 1985 to September 1987, 1374 patients underwent endoscopic retrograde cholangiopancreatography in our Liver Unit. An endoscopic sphincterotomy was indicated in 195 patients with common bile duct (CBD) stones because of an age over 65 years and/or surgical contraindications. Endoscopic sphincterotomy was efficient in 187 patients, allowing complete stone removal in association with conventional endoscopic methods and mechanical lithotripsy in 170 patients. Twelve of the 17 patients with failure of conventional endoscopic treatments were either older than 75 years (11 patients; mean age, 86 +/- 4.5 years) or exhibited a surgical contraindication. Stones completely obstructed CBD in six patients and had a diameter exceeding 25 mm in the six other patients. These subjects were selected for stone dissolution by methyl tert-butyl either (MTBE) according to the following protocol. MTBE was directly infused into CBD through a nasobiliary catheter, twice daily for 4-13 days (mean, seven days). Bile duct opacification, repeated after MTBE treatment, revealed the complete disappearance of CBD stones in one patient, a decrease in stone size in five patients and no change in the six other patients. MTBE treatment was well tolerated except in three patients who complained from transient abdominal pains and nausea. At the second attempt of endoscopic treatment, CBD stones were found to be softened and easily broken up, allowing a complete clearance in six patients.(ABSTRACT TRUNCATED AT 250 WORDS)