The study was aimed to further investigate the role of the midbrain central gray (CG) in the. process of acupuncture analgesia. Tail-flick and screaming in response to electrical stimulation of the tail skin were taken as indices of pain response. The experiments consisted of four groups: (1) surgical control

(2) electroacupuncture

(3) electrical stimulation of CG

and

(4) simultaneous use of stimulation of CG and electro-acupu- ncture. The pain threshold in the experimental groups increased significa- ntly after electroacupuncture or/and brain stimulation. The pain threshold value of the fourth group was much greater than the summation of that of the second and the third group. The regions of brain being stimulated to produce analgesia were found to locate in the lateral and ventrolateral po- rtions of the caudal CG. This work indicated that there was a synergic action between the analgesic effects produced by stimulation of CG and electro-acupuncture.