This experiment is to investigate the electro-acupuncture analgesia on thefluctuations of substance P in brain and spinal cord. The electro-acupuncturewas given to the experimental rats and the quantity of the substance P (SP)in the hypothalamus, the brain stem and the lumber spinal cord was determinedby the radioimmunoassay. The control group was not given the electoacupunctureand the other treatments were the same as the experimental animals. Whilepain threshold increased (PTI) rats with the control were compared; the SP inthe hypothalamus of the PTI rats decreased singnificantly, however the SP in