Our recent studies have demonstrated that needling in Baihui, Shuigou and Shenmen enhances glucose metabolism in the frontal lobes, thalamus, temporal lobe, and the lentiform nucleus in vascular dementia. This study examined the effect of true, sham and overt needling in Waiguan (TE5) on cerebral changes by positron emission tomography (PET) technique. Eighteen healthy volunteers were randomized to receive overt control, true or sham needling therapy. To manipulate true needling, a needle was inserted into 15+/-2mm into Waiguan and "deqi" was achieved by proper needle manipulation. For sham needling, needles with a blunt tip were pushed against the skin as the shaft moved into the handle, giving an illusion of insertion. For overt placebo, blunt needles were used and subjects did not receive any needling penetration. The tracer used was (18)fluoride-deoxygluocse. PET images obtained were processed and analyzed by the SPM2 software. Compared with overt needling, brain areas BA7, 13, 18, 19, 21, 22, 27, 38, 40, 42 and 45 in Waiguan true needling group were significantly activated and areas BA4, 6, 7, 19, 22 and 41 in sham needling group showed obvious activation. Compared to sham needling group, marked activation points were found in the areas of BA13 and 42 and left cerebellum in true needling group. Our study revealed a marked difference in brain metabolic changes between true and sham needling in Waiguan. Further studies are needed to explore the cerebral changes in patients with acupuncture and the pathological implications.