This study was performed to evaluate the effects of enalapril, an angiotensin converting enzyme inhibitor and losartan an angiotensin II receptor antagonist on the level of plasma nitrate in untreated essential hypertensive patients. The study was carried on 28 mild or moderate essential hypertensive patients (9 of them were men, mean age: 46±8 years). After the clinical and plasma nitrate level assessment, patients were randomised to one of the 2 treatment protocols: enalapril 20 mg/d to group I, losartan 50 mg/d to group II. After patients were given antihypertensive treatment for 8 weeks, clinical and plasma nitrate level controls were performed again. Two treatment protocols were observed to decrease the clinical blood pressure meaningfully. With enalapril treatment, the level of plasma nitrate increased from 13.20±4.75 μM/L to 13.71 ±5.71 μM/L (p>0.05). With losartan treatment, the level of plasma nitrate rose from 14.09±5.21 μM/L to 15.12±8.77 μM/L (difference not significant). Thus both enalapril and losartan treatment were thought to increase the level of plasma nitrate in untreated essential hypertensive patients. We believe that randomised studies with larger patient populations should be conducted to evaluate the effect of antihypertensive treatment on plasma nitrate level.