This is a case report of methemoglobinemia presumably caused by the combined use of prilocaine (propitocaine) and nitroglycerin under general anesthesia. Methemoglobinemia is reportedly caused by the administration of prilocaine at a dose of ≥8 mg/kg. Moreover, ≥3 μg/kg/min of nitroglycerin can also trigger methemoglobinemia. In this patient, methemoglobinemia occurred despite neither drug having been administered at the aforementioned doses. Even if individual doses of drugs predisposed to causing methemoglobinemia are low, combined use may increase the risk of methemoglobinemia.