120 patients scheduled to undergo elective orthopaedic surgery were randomized to receive either 0.5 mg/kg ketamine with 0.25 mg/kg/h of continuous ketamine infusion for 30 minutes, or 0.5 mg/kh 0.9% saline with 0.25 mg/kg/h of continuous saline infusion for 30 minutes. The purpose of this study was to determine the effects of intraoperative ketamine administration on patients' postoperative depressive mood using the Patient Health Questionnaire-9 (PHQ-9). Serum brain-derived neurotrophic factor (BDNF) level, intraoperative blood loss, operative time, postoperative visual analogue scale (VAS) pain scores and perioperative complications were also assessed. Findings indicated significantly improved PHQ-9 scores for depressive moods, as well as increased serum BDNF levels and reduced VAS scores after intraoperative ketamine compared to intraoperative saline.