The scope of effectiveness of acupuncture in relieving pain was tested in an Acupuncture Clinic for nonemergency care: 129 patients were treated, mainly for intractable pain associated with a wide variety of conditions. Only mechanical stimulation was used. Acupuncture anesthesia was not evaluated. Response was excellent or good in 87 patients. Acupuncture was most effective in conditions attributable to musculoskeletal or visceral muscle spasm. In some situations it inhibited pain recurrence, such as menstrual cramps in subsequent periods. It did not mask pathology: pain recurred promptly if underlying stimulus persisted. Relief of pain was usually immediate; side effects were negligible. Neurophysiologic principles appear to offer a basis for explaining the mechanism of action. Acupuncture is sufficiently promising as an adjunct to standard medical methods to deserve clinical and theoretical investigation.