In two experimental studies we sought preliminary information about the behavior of concrements lost in the peritoneal cavity during laparoscopic cholecystectomy. Materials and Methods: In study 1, human gallstones were analyzed using X-ray diffraction, calssified in three groups and examined with an ultramicroscope; then they were implanted in the peritoneal cavity of rats. After 8 weeks or 6 months, the animals were sacrificed and the concrements analyzed again as before. The tissues surrouding the calculi were also examined histologically. In study 2, human gallstones were examined with regard to bacterial contamination on the surface or in the middle of the calculi. The cholesterol content was analyzed, and the stones were divided into three groups and implantated in the rats as in the first study. After 8 weeks, the animals were sacrificed and areas with identifiable tissue reactions were examined histologically and microbiologically. Results: The concrements lost their crystalline formation without any relation to their former cholesterol content, as shown by X-ray diffraction as well as ultramicroscopy. Mineralogically, these changes are a certain sign of structural dissolution. Cholesterol stones only caused abscess formations in association with gram-negative bowel germs. Sterile pigment concrements often led to a mesenchymal reaction such as granulomas. Contaminated pigment stones also resulted in extensive abscess formations.