In this study, radioimmunoassay (RIA) was perfomed to measure the contents of opiate peptide in plasma in control group and essential hypertension (EH) group before and after treatment. The relationship between the changes in opiate peptide content and mean artery pressure (MAP) was analysed. The results showed that the contents of ?-endorphin (?-EP) and leuenkephalin (LEK.) in the EH group were lower significantly (P