PURPOSE: The purpose of this study was to compare the effects of intravenous fluid warming and skin surface warming on peri-operative body temperature and acid base balance of abdominal surgical patients under general anesthesia. METHOD: Data collection was performed from January 4th, to May 31, 2004. The intravenous fluid warming(IFW) group(30 elderly patients) was warmed through an IV line by an Animec set to 37 degrees C. The skin surface warming(SSW) group(30 elderly patients) was warmed by a circulating-water blanket set to 38 degrees C under the back and a 60W heating lamp 40 cm above the chest. The warming continued from induction of general anesthesia to two hours after completion of surgery. Collected data was analyzed using Repeated Measures ANOVA, and Bonferroni methods. RESULTS: SSW was more effective than IFW in preventing hypothermia(p= .043), preventing a decrease of HCO3-(p= .000) and preventing base excess(p= .000) respectively. However, there was no difference in pH between the SSW and IFW(p= .401) groups. CONCLUSION: We conclude that skin surface warming is more effective in preventing hypothermia, and HCO3- and base excess during general anesthesia, and returning to normal body temperature after surgery than intravenous fluid warming; however, skin surface warming wasn't able to sustain a normal body temperature in elderly patients undergoing abdominal surgery under general anesthesia.