Hypertension continues to be a major public health issue in the world. To combat this problem, many antihypertensive drugs have been developed and proven effective at controlling blood pressure in the last half century. In recent decades, antihypertensive drugs have been shown to have cardiovascular benefits beyond the reduction of blood pressure, and the focus has shifted to clarification of these effects. Angiotensin II receptor antagonists and calcium channel blockers are the most widely used antihypertensive drugs in Japan. However, these two classes of drugs have not yet been compared with respect to their efficacy for treating cardiovascular events. The Candesartan Antihypertensive Survival Evaluation in Japan (CASE-J) trial described herein is a prospective, multicenter, randomized, open-label, active-controlled, 2-arm parallel group comparison with a response-dependent dose titration and blinded assessment of endpoints in high-risk hypertensive patients treated with either an angiotensin II receptor antagonist (candesartan cilexetil) or a third-generation calcium channel blocker (amlodipine besilate). The eligibility criteria in this study were 1) age between 20 and 85 years; 2) systolic blood pressure (SBP) ≥140 mmHg in those below 70 years of age or ≥160 mmHg in those above 70 years of age or diastolic blood pressure (DBP) ≥90 mmHg on two consecutive measurements at clinic; and 3) at least one of the following high risk factors for cardiovascular events: a) SBP ≥180 mmHg or DBP ≥110 mmHg on two consecutive visits, b) type 2 diabetes mellitus (fasting blood glucose ≥126 mg/dl, casual blood glucose ≥200 mg/dl, HbA1c ≥6.5%, 2 h blood glucose on 75 g oral glucose tolerance test (OGTT) ≥200 mg/dl, or current treatment with hypoglycemic therapy), c) history of cerebral hemorrhage, cerebral infarction, or transient ischemic attack until 6 months prior to the screening, d) left ventricular hypertrophy on either echocardiography or ECG, angina pectoris, or history of myocardial infarction until 6 months prior to screening, e) proteinuria or serum creatinine ≥1.3 mg/dl, and f) symptoms of arteriosclerotic artery obstruction. The therapeutic goals of blood pressure control were set as follows: SBP<130 mmHg and DBP<85 mmHg for patients below 60 years of age, SBP<140 mmHg and DBP<90 mmHg for those in their 60 s, SBP<150 mmHg and DBP<90 mmHg for those in their 70 s, and SBP<160 mmHg and DBP<90 mmHg for those in their 80 s. A total of 3,200 patients, equally allocated to each of the two treatment arms, were required based on a two-sided α level 0.05 and 90% power. The CASE-J is also the first study to employ the newly developed Automatic Bar Code Data-Capturing/Allocation, Booking & Trial Coding, Data Management^TM (ABCD^TM) system for data collection and management. Enrollment of patients started in September 2001 and ended in December 2002. Follow-up data will be collected every 6 months until December 2005. The CASE-J trial will provide important evidence on the comparative effectiveness of candesartan cilexetil and amlodipine besilate on cardiovascular morbidity and mortality among Japanese. In addition, the use of the ABCD^TM system is expected to contribute to the development of more efficient data management systems for large-scale clinical trials. (Hypertens Res 2003; 26: 979-990)