Mounting evidence supports the contention that atherosclerosis is an inflammatory disease. Recently a possible role for infectious microorganisms has gathered attention. Chlamydia pneumoniae is one possible pathogen. If C. pneumoniae is a target organism, antibiotics with antichlamydial activity may be able to ameliorate plaque instability. The WIZARD trial is a secondary prevention study that is assessing the impact of a 3-month course of azithromycin compared with placebo on the progression of clinical coronary heart disease. The study will enroll 3300 patients who have had a prior myocardial infarction and who have a C. pneumoniae IgG titer of >/=1:16. The primary end point is a composite of time to either recurrent myocardial infarction, death, a revascularization procedure, or hospitalization for angina. This study is the first of a series of adequately powered clinical trials that will attempt to bridge insights from preclinical investigations to interventions applicable to patient care.