Arginase activity in erythrocytes is higher in patients with arterial hypertension and atherosclerosis as compared with healthy people. Therapy with either lisinopril alone or in combination with simvastatin for 3-6 months causes a decrease in the arginase activity to the control level. Both the monotherapy and the combination therapy increased the concentrations of NO2(-), NO3(-), and total NOO2(-) + NO3(-)in the plasma of hypertensive patients. The NO2(-) + NO3(-) concentration in erythrocytes decreases in hypertensive patients but is completely restored after therapy with lisinopril alone or in combination with simvastatin. Thus, lisinopril and lisinopril plus simvastatin display a pronounced and equal normalizing effect on arginase activity in human erythrocytes, which is elevated in hypertension, as well as on the endothelial nitric oxide synthase activity, which is decreased in hypertension.