This research work allowed the development of a scientific approach to a remedy widely used until today in ranches or rural posts as an alternative medicine: The "guanaco stone" or bezoar. Bezoars are compactions of various chemical substances, hairs, vegetable fibers and foreign bodies, which are formed mainly between the divisions of the stomach of guanacos (Lama guanicoe). The ethnomedicine of this Patagonian region uses powdered bezoars ingested with water or in infusions, as a medicine that improves digestive and renal functions, and especially alexipharmaceuticals. The objective of this trial was to find "in vitro" the pharmacological foundations of bezoars. Samples of bezoars, obtained from the local refrigerator, were used in the test. For this, its density, colors, hardness were determined. One of the bezoars was totally pulverized, the powder obtained was observed under an optical microscope with a magnification of 1000X. Subsequently, the chemical composition was sought by examining the presence of P, K and N, as well as the pH. The results made it possible to determine the pH is neutral and the presence of P, N, and K is medium. It is concluded in this first approach to the subject that according to these determinations, bezoars can act by two mechanisms: the presence of phosphates acts as chelators of ingested toxins, facilitating their elimination from the body, but also the minerals that together stimulate the secretion of acid gastric and digestive enzymes.