We report a series of 10 elderly patients with large bile duct calculi refractory to standard endoscopic extraction techniques who were treated by gall stone dissolution using methyl tertiary butyl ether (MTBE) instilled through a nasobiliary catheter. In eight patients complete bile duct clearance was achieved after an average of eight hours MTBE instillation. In two patients gall stone size did not change. Both underwent operative gall stone removal and subsequent stone analysis showed low cholesterol content, which is unlikely to respond to MTBE. Apart from occasional transient nausea and drowsiness, no adverse reactions were noted. Methyl tertiary butyl ether appears to be a powerful in vivo gall stone dissolution agent which, from preliminary studies, is not associated with serious toxicity.