Renin–guided therapeutics using plasma renin activity (PRA) values may lead to clinically significant blood pressure (BP) reductions. We were to compare the effect of renin-guided therapy versus (not renin-based) routine practice on short-term BP reductions in young untreated hypertensive patients who mostly have high renin activity would benefit from renin-targeted antihypertensive drugs. Thirty-two young untreated hypertensive patients less than 55 years old were randomized to either renin-guided group (PRA group, n=16) or routine practice (Control group, n=16) managed by different specialists in hypertension clinic. After the blood samples for PRA were drawn at the first visit, randomization was made after one week. PRA group received antihypertensive drug based on their PRA, i.e. either angiotensin converting enzyme inhibitor or angiotensin receptor blocker if their PRA ���0.65 ng/ml/h, calcium antagonist or diuretics if PRA< 0.65 ng/ml/h. Control group received antihypertensive drug selected by a specialist blinded to PRA value. If the BP has not reached the goal (<140/90mmHg) after 2 months, both group received another class of antihypertensive drugs added. The study subjects were 45 years old in average (from 33 to 54). PRA group had similar initial BP (systolic BP, 156.8짹14.5 vs 166.9짹18.2 mmHg; diastolic BP, 97.7짹10.7 vs 102.9짹12.3 mmHg) and showed similar BP reduction after one year study period (systolic BP, 126.2짹9.4 vs 128.0짹10.5 mmHg; diastolic BP, 80.8짹6.1 vs 78.4짹7.2 mmHg) compared to Control group. In conclusion, plasma renin-guided treatment in young untreated hypertension does not seem to be more effective for the short-term BP reduction than the routine practice independent of PRA value.