The effect of circulating arginine vasopressin (AVP) on blood pressure, heart rate and skin blood flow was investigated in 8 untreated patients with mild essential hypertension using a specific antagonist of the pressor effect of AVP. Skin blood flow was measured with a laser Doppler flowmeter and blood pressure with a Remler M2000 recorder. The study was carried out in double-blind fashion using a cross-over design. Each patient received at a 60 min interval the AVP-antagonist, d(CH2)5Tyr(Me) AVP, 5 micrograms/kg i.v., and its vehicle. The sequence of treatment phases was randomly allocated. Pretreatment plasma AVP levels averaged 1.1 +/- 0.2 pg/ml (mean +/- SEM). Neither the AVP-antagonist nor its vehicle had any effect on blood pressure, heart rate and skin blood flow as well as on plasma renin activity and plasma catecholamines. It is therefore concluded that circulating AVP does not contribute to the maintenance of blood pressure in patients with mild essential hypertension and normal plasma AVP levels.