Piridoxilate (P) is given in cases of angina pectoris or arteritis. It is an intramolecular association of glyoxylic hemiacetal salts of pyridoxine. Glyoxylate has a membranous protective action; pyridoxine is used for the theoretical purpose of preventing oxidation of glyoxylic acid to oxalic acid. We have observed 12 patients with an active calcium oxalate lithiasis who had been taking P for many years. Hyperoxaluria was present in all patients and decreased significantly when the drug was interrupted. Significant hyperoxaluria was also observed in volunteers after ingestion of P (600 mg per day) or i.v. (200 mg). We have obtained experimental calcium oxalate urinary stones after intraperitoneal injection of P to Wistar rats. Piridoxilate represents an important lithogenic factor.