BACKGROUND How far should blood pressure (BP) be lowered to achieve the greatest reduction in the risk of cardiovascular disease? Although a few trials have tried to answer this question, they failed to convincingly establish an optimal target BP level, in part because of poor reproducibility and the wide variability of conventional casual BP measurement they used. At the same time, in Japan, calcium antagonist (Ca-A) and angiotensin-converting enzyme inhibitor (ACE-I) have been two major medications in initial therapy for hypertension, while angiotensin II receptor antagonist (ARB), which has recently been introduced, is also now used widely as an initial therapy. However, no large-scale interventional trial has been conducted to show which of these three initial medications can give the greatest benefit in reducing the risk of cardiovascular disease in the Japanese hypertensive patient. OBJECTIVE The objectives of the study are, first, to determine an optimal target BP level, based on BP values self-measured at home (home BP). This way of measurement provides more reproducible and less variable BP values than conventional casual measurements. Secondly, we seek to determine the optimal initial antihypertensive medication for the Japanese hypertensive population. METHOD The study is a 2 x 3 factorial randomized controlled trial conducted with a prospective randomized open-blinded endpoint design. The study will include a total of 9000 untreated essential hypertensive patients aged 40 to 78 years with home BP values > or = 135/85 mmHg. Eligible patients are randomized to one of the two home BP target groups (systolic/diastolic home BP within the range of 134-125/84-80 mmHg, or > or = 125/80 mmHg), and to regimens based on one of three initial antihypertensive drugs (Ca-A or ACE-I or ARB). These randomizations, performed by our host computer, are transmitted to terminals at the outpatient clinic through the Internet. The patient measures BP at home with newly developed equipment (HEM-7471C-N; Omron, Japan) that records BP values, the date, and the time of each measurement. The data are downloaded to the outpatient terminal at every clinic visit then transmitted to the host computer via the Internet. Based on these home BP values, the host computer determines the necessity of additional therapy or dose increments in four further steps to reach the randomized target BP, and then transmits the information to the terminal at the outpatient clinic. The primary study outcome is a composite of non-fatal stroke, non-fatal myocardial infarction, and cardiovascular death. The scheduled average post-randomization duration of follow-up is 7 years. CONCLUSION This is the first large-scale home BP-based and Internet-connected intervention trial on antihypertensive treatment. The HOMED-BP study (Hypertension Objective treatment based on Measurement by Electrical Devices of BP) will improve the recruitment of general practitioners and participants and will supply unbiased BP data, providing reliable information on optimal target BP levels and the optimal initial antihypertensive medication.