Objectives In order to study the endogenous opioid polypeptides involved in pathogenesis of epidemic encephalitis-B and the clinical therapeutic efficacy.Methods ①Leucine-enkephalin,?-endophin and Dynorphin levels in plasma and and CSF of patients with epidemic encephalitis-B during critical stage and convalescent stage were measured by radio-immunoassay.②Naloxone therapeutic efficacy in patients with epidemic encephalitis-B were investigated.Results Opioid polypeptides levels In plasma and CSF were significantly higher in critical stage and dropped to normal levels in convalescent stage.③We demonstrated that endogenous opioid polypeptides special antagnoist agent-Naloxone was a very important therapy agent for epidemic encephalitis-B patients.Therapy group efficacy was significantly better than control group.Conclusions These results demonstrate that endogenous opioid polypeptides involves in the physiopathologic changes of epidemic encephalitis-B.