A prospective controlled trial comparing the efficacy of heparin and monooctanoin as solvents of retained common bile duct stones through the T‐tube is presented. The results were compared to those obtained by the saline washout technique which was used as a retrospective comparison group. After treatment, 33% and 65% of the patients treated with heparinized saline solution and monooctanoin, respectively, showed absence of stones on cholangiograms (p<0.01). In patients submitted to the washout technique, 20% of 54 patients who completed the treatment showed disappearance of stones. Side effects during infusion were more serious in the monooctanoin group and 1 patient developed sepsis in this group. The results of the present study strongly suggest that monooctanoin may be a reasonable alternative treatment for those patients who show residual common bile duct stones after surgery.