The presence of humic and fulvic acids in the Anticolana Valley (Fiuggi) water has been established. On the basis of this evidence we investigated the capacity of Anticolana Valley (Fiuggi) water to dissolve renal calculi in vitro. Crystals of calcium oxalate monohydrate to simulate a kidney stone were prepared. Human renal stones of calcium oxalate monohydrate were obtained by courtesy of the Division of Urology of 'La Sapienza' University (Rome), the Division of Urology of the University of Havana (Cuba) and the ASTIF of Fiuggi. The study was performed using the Anticolana Valley (Fiuggi) water, distilled water and tap water (ACEA, Rome), in a specially designed Perspex apparatus. Each calculus was subjected to a water flow of 2 liters/24 h. The capacity of the Anticolana Valley (Fiuggi) water to dissolve human and synthetic calculi was found to be much higher than that of distilled water which in turn was significantly more effective than tap (ACEA) water.