Eighty-five patients suffering from acute pain in the head

shoulder and back-leg region were stu-died.Acupuncture points were selected according to symptom analysis based on the Channel theory oftraditional Chinese medicine.Generally

the needles were twisted for several seconds to one minuteand then retained in position for 20 minutes.The effects of acupuncture treatment on pain were divided into the excellent or the poor effectivegroup according to the degree of pain relief after needle removal.The differences of microvascularchanges between these two groups were observed.Whatever the analgesic effect of acupuncture

inser-ting and twisting needles caused a transient vasoconstrictive reaction in several regions of the body.During the first five minutes of needle retention

in 47 cases with the excellent analgesic effect

themicrovessels near the sore point slightly dilated in 41 cases

unchanged in 5 cases and constricted in2 cases.However

in the remaining 38 cases with poor analgesic effect

near the sore region markedvasoconstriction was observed in 23 cases;no change in 5 cases;vasodilation in 10 cases.Microvascu-lar changes at the regions far from the painful area always appeared later than at those near the sore.The vasodilatory reaction in the great majority of the patients with excellent analgesic effect was conti-nuously maintained for more than 20 minutes after needle removal.It is presumed that the activatingway of acupuncture may affect the sympathetic vasomotor fibres in the painful regions to modulatethe excitability of the afferent nerve endings to the painful sensation.