BACKGROUND/AIMS: We investigated whether the presence of bile changes the cholesterol dissolving capacity of methyl-tert-butyl ether (MTBE) or ethyl propionate (EP) and dimethylsulphoxide (DMSO) enhances the cholesterol dissolving capacity of MTBE or EP solvent when cholesterol gallstones were dissolved with bile. METHODS: We mixed MTBE (or EP) with water or bile. Then, pure choestero was dissolved in this solvent and its concentration was measured by cholesterol kit. MTBE/DMSO and EP/DMSO mixtures were prepared and added to different amount of bile and cholesterol. The cholesterol concentration of these mixtures were determined by cholesterol kit. The eight weight-matched cholesterol gallstones were selected and divided into two groups. One group was fo MTBE/bile and MTBE/bile/DMSO mixtures and another group was for EP/bile and EP/bile/DMSO mixtures. Each stones were placed in test tube with each solvents. Creating turbulence manually 4-6 cycle a minute, the solvent and bile were exchanged every 15 minutes and stones were dried and weighed until complete dissolution. We measured complete dissolution time or weight percent of remained stone 300 minutes later. RESULTS: The presence of bile or water decreased cholestero dissolution capacity of MTBE and EP by 33-42%. Addition of DMSO to MTBE/bile enhanced cholesterol dissolving capacity and shortened cholesterol stone dissolution time by 43%. Addition of DMSO to EP/bile increased cholesterol stone dissolving capacity by 15.3%. CONCLUSIONS: MTBE/DMSO is more potent and useful dissolution agent for cholesterol gallstone than MTBE alone unde bile milieu, giving a reduction in dissolution time.