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This study examined whether local anesthetics react with superoxide (O・/2) radicals and generate other oxygen radicals. Lidocaine, mepibacaine, prilocaine, and dibucaine were used as amido type anesthetics ; procaine, and tetracaine as ester type anesthetics ; and epinephrine and ephedrine as epinephrine-like substances. A hypoxanthine-xanthine oxidase (HPX-XOD) reaction system was employed as the O・/2 generator. Detection and measurements were carried out with the ESR spin trapping method. When amido type anesthetics were added with epinephrine, alkoxyl (RO・) and hydroxyl (HO・) radical generation was confirmed, but there was no RO・ and HO・ generation with ephedrine. With ester type anesthetics with epinephrine, there was no RO・ generation. The signal intensities of RO・ and HO・ were dependent on the concentration of anesthetics and epinephrine. These results show that RO・ and HO・ generation by local anesthetics occur only where amido type anesthetics, cathecols, and (O・/2) are present.