Objective To evaluate the effects of parecoxib on cellular immune function during patientcontrolled intravenous analgesia (PCIA) with butorphanol after modified radical mastectomy in patients.Methods Sixty ASA physical status Ⅰ or Ⅱ patients,aged 36-60 yr,weighing 48-82 kg,scheduled for elective modified radical mastectomy,were randomly divided into 2 groupe (n =30 each):control group (group C) and parecoxib group (group P).PCIA with butorphanol 10μg/kg was used at the end of operation.The PCIA pump was set up to deliver a 0.5 ml bolus dose with a 15-min lockout interval and background infusion at 2 ml/h.In group P,parecoxib 40 mg was injected intravenously at the end of operation and 12,24 and 36 h after surgery,while in group C,the equal volume of normal saline was injected.VAS score was maintained at ≤4.When VAS score≥5,butorphanol was injected intravenously as a rescue analgesic.Blood samples were obtained from the right internal jugular vein at 5 min before induction of anesthesia,2 h after skin incision,and 6 h and 1,3,7 days after surgery for determination of the levels of T lymphocyte subsets (CD3+,CD4+,CD8+,CD4+/CD8+) and natural killer (NK) cells (by flow cytometry).CD4+/CD8+ was calculated.The number of attempts,the number of successfully delivered doses and requirement for rescue analgesics were recorded at 2,6,12,24 and 48 h after surgery.Adverse effects were also recorded after surgery.Results Compared with group C,the number of attempts and requirement for rescue analgesics were significantly decreased,the number of successfully delivered doses was increased,and the levels of CD3+,CD4+,CD4+/CD8+ and NK cells were decreased at 1 day after surgery (P ＜ 0.05).There was no significant difference in adverse effects between the two groups (P ＞ 0.05).Conclusion Parecoxib can enhance the efficacy of postoperative PCIA with butorphanol and reduce the consumption of butorphanol thus improving cellular immune function after modified radical mastectomy in the patients.