This study represents the first attempt to simultaneously explore the comprehensive relationship between acupuncture, circulating endorphins, and relief of both the pain and psychiatric symptoms of the chronic pain syndrome in a well-defined patient group. Our results indicate that acupuncture is effective in relieving both the pain and the psychiatric symptoms of this illness, and that its effectiveness is correlated with increases in plasma met-enkephalin immunoreactivity. It should also be noted that we cannot infer that the clinical and biochemical results seen in our study are specific for acupuncture. Our results could also be explained by the placebo effect, which has been proposed to involve endorphins (56,57). Studies to test this hypothesis are currently under way in our laboratories.