The effects of free radicals on the development of crystals attached to the living epithelium have been studied using an experimental model that enables close simulation of the conditions prevailing in the kidney. The results obtained clearly demonstrate that free radical-damaged cells produce a favorable environment for crystal development. At low free radical concentrations, crystals develop on calcium-enriched zones, whereas at higher concentrations, crystals develop on areas with a destroyed monolayer of superficial cells. Evaluation of the action of some products with antioxidant action and/or crytallization-inhibitory capacity is also included. Antioxidants, such as ascorbic acid and mannitol, exerted the most remarkable effects in avoiding calcium oxalate crystal development, whereas crystal inhibitors, such as citric acid, did not produce any remarkable reduction in calcium oxalate crystallization. Phytic acid notably decreased calcium oxalate crystal development. The ability of phytic acid to diminish calcium oxalate crystallization must be attributed to the combination of its inhibitory capacity of calcium oxalate crystallization and its preventive antioxidant action.