Background Other than aspirin, there are few oral antithrombotic treatments with proven efficacy in patients with acute coronary syndrome. In this report, we present the rationale, design and baseline characteristics of the Clopidogrel in Unstable angina to prevent Recurrent ischaemic Events (CURE) trial, which includes a meta-analysis of the effects of thienopyridines in patients with vascular disease. Methods and Results Combined data from randomized trials of thienopyrindines in patients with atherosclerotic disease demonstrated a 29% reduction in vascular events when compared with placebo/control (n=2392) (OR 0.71, 95% CI 0.58-0.86, P=0.0006) and a 10% reduction in vascular events when compared with aspirin (n=22 254) (OR 0.91, 95% Cl 0.84-0.99, P=0.039). Similarly, randomized trials of aspirin plus thienopyridines in patients undergoing intracoronary stenting, demonstrated marked benefit of aspirin plus ticlopidine in reducing death or myocardial infarction compared with aspirin alone (OR 0.23, 95% CI 0.11-0.49, P=0.0001) or aspirin plus warfarin (OR 0.51, 95% CI 0.33-0.78, P=0.002). Whether these benefits extend to the much larger population of patients with acute coronary syndrome is unknown. CURE is an international, randomized, double-blind trial, in which patients with acute coronary syndrome will be randomized to receive either a bolus dose of clopidogrel (300 mg) followed by 75 mg per day for 3-12 months, or matching placebo. Both groups will receive aspirin. The co-primary efficacy end-points of CURE are: (1) the composite of cardiovascular death, myocardial infarction or stroke; and (2) the composite of cardiovascular death, myocardial infarction, stroke or refractory ischaemia. CURE will recruit approximately 12 500 patients with acute coronary syndrome (from 28 countries) and its power to detect moderate treatment benefits will be in the region of 80-90%, while maintaining an overall type I error (a) of 0.05. The baseline characteristics of the study population are consistent with at least a moderate risk group of patients with acute coronary syndrome. Conclusions Randomized trials of thienopyridines in patients with vascular disease demonstrate that thienopyridines are effective in reducing vascular events when compared with placebo/control or aspirin, as well as when used in combination with aspirin in patients undergoing intracoronary stent implantation. The CURE trial is a large international study to determine if acute and longterm treatment with the combination of clopidogrel and aspirin is superior to aspirin alone in patients with acute coronary syndrome. (C) 2000 The European Society of Cardiology.