We produced the cauaalgiform pain by unilateral 1/3-1/2 ligation of sciatic nerve in rats.. Withdrawal thresholds to non-noxious stimulation were reduced(mechanical allodynia), and withdrawal thresholds to heat stimulation were reduced(heat hyperalgesia) too. After that, we injected 50 mg/kg guanethidine intraperitoneally for the study of the effects of chemical sympathectomy in postopertive 7th day, 37th day respectively. The results were as follows 1) Mechanical allodynia was alleviated partially in 12 hours, first day after sympathectomy. 2) Heat hypera1gesia was alleviated completely in first day to 4th day after sympathectomy, and reappeared after 5th day.