['Although endoscopic submucosal dissection (ESD) for patients with gastric tumors under the conditions of unconsciousness is considered to be minimally invasive, no objective assessment of the perioperative stress of ESD has yet been conducted. Today, stress levels can be easily and objectively assessed by monitoring salivary amylase activity (sAMY). We evaluated the perioperative changes in the sAMY in patients undergoing ESD and identified the causes of such changes.', 'A total of 40 patients with gastric cancers/adenomas removed by ESD under general anesthesia (GA; n = 20) and under deep sedation (DS; n = 20) were enrolled. sAMY was measured using the enzyme analysis equipment, sAMY Monitor (NIPRO, Osaka, Japan) during the perioperative period of the ESD. Also, all patients were interviewed to determine their subjective stress level, using a questionnaire asking "How did you feel during ESD?", with the choice of responses ranging from "did not wake up at all" to "I was awake and ESD was extremely stressful".', 'The sAMY of the DS group increased soon after the start of ESD. Meanwhile, that of the GA group decreased just after the ESD started and was maintained at a stable level throughout the ESD. In response to the stress level questionnaire, all of the patients in the GA group and a majority of the patients in the DS group responded, "did not wake up at all".'] Is salivary amylase activity useful for assessing perioperative stress in response to pain in patients undergoing endoscopic submucosal dissection of gastric tumors under deep sedation?