In order to investigate the effects induced by acupuncture on the activity of enkephalinergic neurons in the spinal cord, either the lumbar or the cervico-trigeminal area was perfused with artificial cerebrospinal fluid (CSF) (0.1 ml/min) in halothane-anaesthetized rats, and Met-enkephalin-like material (MELM) was measured in 0.5 ml fractions of the perfusates. The effects of manual acupuncture performed by a traditional Chinese acupuncturist at the 'Zusanli' point on the right hind limb were compared to the effects induced by acupuncture applied at a non-acupoint next to 'Zusanli.' The manipulation of needles either at the 'Zusanli' point or at the non-acupoint had no effect on the release of MELM from the lumbar area but significantly increased the release from the cervico-trigeminal zone. It is concluded that manual acupuncture triggers a heterosegmental activation of enkephalinergic neurones within the spinal cord and that this effect is non-specific in terms of the location of the stimulated point.