We observed the effects of intravenous administration of L-arginine on plasma concentration of L-arginine and blood pressure in 15 patients with essential hypertension and 14 normotensive control subjects.Intravenous administrate of L-arginine increased the plasma concentration of L-arginine and decreased mean blood pressure in both groups. There results suggest the effects of exogenous L-arginine supplementation on mean blood pressure are similar in the two groups.