Coronary heart disease remains the most common cause of death in industrialized countries. Although atherosclerosis is generally asymptomatic in the early stages, progressive plaque development leads to arterial stenosis which is characterized by angina and may eventually lead to unstable angina, myocardial infarction and cardiac death. Evidence that the coagulation cascade is activated during acute coronary events has justified the use of antithrombotic agents such as aspirin, heparin and low molecular weight heparin (LMWH) in the standard management of acute coronary syndromes. The inflammatory process is also known to play a significant role in the pathogenesis of atherosclerosis, resulting in a cycle of continued inflammatory cell activation and ongoing cell recruitment. As the human leukocyte-associated antigen (HLA) system plays a key role in the regulation of the inflammatory process, the expression of HLA antigens in patients with symptomatic coronary heart disease has been investigated. These studies have demonstrated a relationship between the major histocompatibility complex (MHC) class II expression and the most severe pattern of angina refractory to conventional therapy, within the framework of a chronic infectious disease. A number of studies have documented an association between coronary heart disease and the presence of high titres of antibodies to Chlamydia pneumoniae, and this organism has been implicated in plaque instability. Such findings have stimulated interest in the role of C. pneumoniae in the pathogenesis of coronary heart disease, with a view to developing novel and effective treatment approaches. The ROXIS study showed a lower incidence of acute ischaemic events in patients with unstable angina treated with an antichlamydial antibiotic, roxithromycin.