In vitro and in vivo experiments were carried out with medium-chain glycerides. In vitro, cholesterol gallstones were rapidly dissolved by medium-chain glycerides; control experiments with saline solution failed to modify the size of the stones. In vivo, medium-chain glycerides were instilled through an intraductal tube in 12 patients with retained bile duct stones. Perfusions lasted 2-10 days. After perfusion, stones disappeared in six cases, were reduced in size in one case, and remained unchanged in five cases. In five cases, nausea, vomiting, diarrhea, or pain were observed. Medium-chain glyceride infusion rapidly dissolves cholesterol gallstones, but is commonly associated with mild to severe side effects.