Abstract: AIM To observe the effect of amlodipine plus telmisartan on mild to moderate hypertension and to explore the changes of arginine vasopressin (AVP) and nitric oxide (NO) and their relationship to the therapeutic results in patients with essential hypertension. METHODS Sixty cases of mild to moderate hypertensive patients were randomly divided into: amlodipine group, telmisartan group and amlodipine+telmisartan group (n=20, each). Blood pressure was measured, and plasma AVP and NO were measured by RIA and colorimetric method before and after treatment. RESULTS After six months’ treatment, systolic blood pressure (SBP) and diastolic blood pressure (DBP) in the three groups decreased significantly (P<0.05). SBP and DBP in amlodipine+telmisartan group were lower than those in amlodipine group and telmisartan group (P<0.05), but no significant difference was observed between amlodipine group and telmisartan group. After one and two months’ treatment, the rate of well-controlled blood pressure in amlodipine+telmisartan group was higher than that in amlodipine or telmisartan group (P<0.05), and no significant difference was observed between amlodipine group and telmisartan group. After six months’ treatment, the plasma NO content increased significantly in the three groups (P<0.05). The plasma NO content in amlodipine+telmisartan group was significantly higher than that in amlodipine group or telmisartan group (P<0.05), with no significant difference between the latter two groups. The plasma AVP content decreased significantly in the three groups (P<0.05). The plasma AVP in amlodipine+telmisartan group was significantly lower than that in amlodipine group or telmisartan group (P<0.05), with no significant difference between the latter two groups. CONCLUSION Though single administration of amlodipine or telmisartan well controls blood pressure, amlodipine combined with telmisartan achieves better results. The decrease of plasma AVP content and the increase of NO content during the drug administration suggest that AVP and NO may participate in the occurrence and development of hypertension. Thus both of them can serve as indicators for curative effects.