This study investigated the effects of intraoperative remifentanil administration on postoperative pain and morphine requirements in patients undergoing major abdominal surgery. Fifty patients were randomly assigned to two groups: one received remifentanil, while the other received desflurane. The remifentanil group required significantly more morphine and experienced greater postoperative pain than the desflurane group. The mean remifentanil infusion rate was 0.3 ± 0.2 μg·kg⁻¹·min⁻¹, which was significantly higher than in the desflurane group. Postoperative pain scores were significantly greater in the remifentanil group, and these patients required morphine significantly earlier and needed nearly twice as much morphine in the first 24 hours post-surgery. The study suggests that remifentanil causes acute opioid tolerance, leading to increased postoperative pain and morphine consumption. This is likely due to the rapid development of acute opioid tolerance, which is more pronounced with short-acting opioids like remifentanil. The findings indicate that remifentanil may be associated with acute opioid tolerance and hyperalgesia. The study also highlights the importance of considering the potential for increased morphine requirements and postoperative pain when using remifentanil in clinical practice. The results support the hypothesis that intraoperative remifentanil administration results in acute opioid tolerance, which is manifested by increased postoperative pain and opioid requirement.This study investigated the effects of intraoperative remifentanil administration on postoperative pain and morphine requirements in patients undergoing major abdominal surgery. Fifty patients were randomly assigned to two groups: one received remifentanil, while the other received desflurane. The remifentanil group required significantly more morphine and experienced greater postoperative pain than the desflurane group. The mean remifentanil infusion rate was 0.3 ± 0.2 μg·kg⁻¹·min⁻¹, which was significantly higher than in the desflurane group. Postoperative pain scores were significantly greater in the remifentanil group, and these patients required morphine significantly earlier and needed nearly twice as much morphine in the first 24 hours post-surgery. The study suggests that remifentanil causes acute opioid tolerance, leading to increased postoperative pain and morphine consumption. This is likely due to the rapid development of acute opioid tolerance, which is more pronounced with short-acting opioids like remifentanil. The findings indicate that remifentanil may be associated with acute opioid tolerance and hyperalgesia. The study also highlights the importance of considering the potential for increased morphine requirements and postoperative pain when using remifentanil in clinical practice. The results support the hypothesis that intraoperative remifentanil administration results in acute opioid tolerance, which is manifested by increased postoperative pain and opioid requirement.