Variations in study results presented in this chapter may be attributed to a number of factors, including the population studied and type of hormonal assay used. Some researchers selected experimental groups from a population different from that used for the control group. It is unclear from the animal studies using nonacupunctured controls whether the controls received physical contacts with the experimenters comparable to those experienced by the experimental animals. The choice of acupuncture points used may also contribute to the inconsistency between experiments, since according to traditional acupuncture theory, points are not equivalent in their mediation of systemic effects. Duration of the acupuncture treatment, frequency of sampling, and time from treatment to last sample were not standardized. There is little consistency between studies even after adjustment for sampling time. Most of the statistically significant changes have been seen with electroacupuncture, and they appear to occur soon after onset of treatment, then disappear within 30 minutes of needle removal. However, the subjective changes in pain threshold have lasted several hours following needle removal. As an analgesic technique or adjuvant, acupuncture has been used most successfully in dental procedures and relatively superficial operations such as thyroidectomy; however, it has also been employed in more complex operations. The blood pressure and heart rate stability that have been observed with acupuncture analgesia have not been sufficiently explained and warrant further investigation, as does the possibility that acupuncture may be helpful in shock states characterized by increased stress hormone concentrations.