Experiments were performed on cats under the treaments of chloralose and Flaxelil.The cortical evoked potentials (C-CEP) which were elicited by C-fibes inputs of saphenous nerve in the somatosensory cortex were used as an index of slow pain.The influence of electro-acupuncture of “Zusanli” point on C-CEP was observed.The results indicated that the electro-acupuncture had an obvious inhibition on C-CEP

which was consisted of two phases:Early inhibition and late inhibition.Naloxone (0.1mg/kg

i.v.) could partially blook the late inhibition on C-CEP but had a little effect on the early inhibition.It was revealed that the early inhibitory effect of electro-acupuncture on C-CEP was different from the late inhibitory on which might be associated with release of endogenous opiate like substances (OLS).