In this paper the averaged cortical evoked potential (C-CEP) induced by stimulating the C-fibers of the splanchnic nerve was used as an index of visceral pain to further study the effects of acupuncture and morphine on it. Experiments were carried out on 35 cats anesthetized with chloralose and immobilized with flaxedil. The splanchnic nerve was stimulated with electric pulses of varied strength and blocked by a galvanic current so as to cause A- or C-fibers input selectively. The cortical evoked potential was recorded on the contralateral postsigmoid gyrus and averaged by TQ- 19 Medical Data Processor. The compound action potential of splanchnic nerve was monitored. "Neiguan" acupoint was stimulated with electric pulses (0.1ms

4v and 5Hz). The results were as follows: 1) when "Neiguan" acupoint was excited with the electric pulses

C-CEP and the late component of A-CEP which was evoked by stimulating A-fibers of splanchnic nerve were obviously reduced in amplitudes. It was suggested that electro-acupuncture (EA) of "Neiguan" acupoint could inhibit visceral pain (the slow and fast pain). 2. After intraveaous injection of morphine

the amplitudes of C-CEP and the late component of A-CEP were depressed significantly

indicating that C-CEP might reflect the visceral slow pain and the late component of A-CEP reflect the fast pain. 3. Naloxone could block partially the inhibitory effect of EA of "Neiguan"acupoint on C-CEP

suggesting that the inhibition of EA might be associated with the release of endogenous opiate like substances.