To determine whether the effect of electroacupuncture (EA) on electroconvulsive shock (ECS) was through affecting endogenous opioid peptidergic system in the hippocampus, we used radioimmunoassay (RIA) to measure leu-enkephalin- and beta-endorphin-like immunoreactivity (L-E-LI and Beta-E-LI) in the hippocampal perfusate after ECS and EA treatments. Wistar rats were given ECS stimulation, which caused behavioral and electroencephalogram (EEG) convulsions. However, EA could suppress ECS-elicited convulsions (including both behavioral and EEG abnormalities). The results of RIA showed that after repeated ECS treatments, the contents of L-E-LI and Beta-E-LI increased significantly by 136% and 157%, respectively. In contrast, EA treatment depleted alterations of L-E-LI and Beta-E-LI induced by ECS, depleting L-E-LI by 32% and Beta-E-LI by 85%. These observations suggest that anticonvulsive action of EA is related to the release of L-E and Beta-E in hippocampus, probably through decreasing their release, thus to exert EA action.