Calcitonin gene-related peptide (CGRP) is a 37-amine acid bioactive polypeptide and known to be a powerful vascular relaxant. CGRP was measured in 45 cases with essential hypertension (EH). The results suggested that plasma CGRP level in patients with EH was lower than that in normal subjects (P less than 0.001). It was found that decrease of plasma CGRP was closely related with the severity of hypertension. However, the level of plasma atrial natriuretic factor (ANF) in EH patients was significantly increased as compared with normal subjects (P less than 0.01). A negative correlation between plasma CGRP and ANF (r = -0.3615, P less than 0.02) was found. These data suggested that decrease of plasma CGRP may play an important role in the pathogenesis of hypertension.