<p>  Methemoglobinemia is reportedly caused by propitocaine administration. According to the clinical statement from the Japanese Dental Society of Anesthesiology, the maximum dose of propitocaine is 400-600 mg (6-8 mg/kg). We experienced a case of propitocaine-induced methemoglobinemia at a dose of 4.3 mg/kg in a 28-year-old woman with a height of 152.8 cm and weight of 50.8 kg. Surgery for placement of a dental implant was scheduled under intravenous sedation. The patient had a diagnosis of schizophrenia and took aripiprazole regularly. We planned to inject 3% propitocaine and 0.03 IU/mL felypressin as local anesthetic because aripiprazole is contraindicated for combined administration of adrenaline. Intravenous sedation was maintained with midazolam and propofol. The patient’s initial SpO₂ was 96% under air, but rose to 94% after administration of 7.2 mL propitocaine. Administration of oxygen resulted in recovery of SpO₂ to 100%, and her final SpO₂ was 96% under air after the need for sedation. However, SpO₂ rose to 91% after 20 min in the recovery room. We started to monitor the hemoglobin concentration ; SpMet^® using a pulse CO oximeter (Rainbow^®, MASIMO Inc.), which was 4.6%. We diagnosed the patient with methemoglobinemia and continued to measure the hemoglobin concentration and this measurement decreased to 2.5% 4h and 25 min after propitocaine injection. We decided to discharge the patient from the hospital because the hemoglobin concentration was lower than normal value ; <3% and the patient strongly wished to be discharged. The patient was ultimately discharged from the hospital without any symptoms of methemoglobinemia.</p>