This work was performed on 72 albino rats immobilized by tubocurarine. Our results suggest that electro-acupuncture might evoke a release of neurotransmitters including noradrenaline and 5-hydroxytryptamine at the level of mesencephalic reticular formation (MRF), so that discharges from the pain-sensitive neurons would be inhibited, the transmission of pain signals could be blocked and an analgesic effect produced. In addition, the results also suggest that, as a neurotransmitter, acetylcholine might probably participate in the transmission of pain signals in MRF and that electro-acupuncture might exert a post-synaptic inhibitory effect on the pain-sensitive neurons in MRF