Six hundred and thirty-eight patients who presented with clinical symptoms and/or electrocardiographic findings suggestive of stable angina pectoris were studied; they were also investigated by coronary arteriography. Hemoglobin electrophoresis was performed on all patients to detect the presence of the beta-thalassemia trait. Results were analyzed by logistic regression analysis to determine whether the latter confers any protective effect against advanced coronary artery disease (aCAD; defined as the presence of atheromas in coronary arteries, resulting in stenosis at least 70%). The role of the currently accepted risk factors (smoking, hypertension, hypercholesterolemia, and diabetes) in developing aCAD were reconfirmed, while at the same time it was found that beta-thalassemia heterozygosity is associated with a reduced risk against aCAD (odds ratio 0.39, 95% confidence interval 0.16-0.98). The lipoprotein and blood rheology profile of these individuals may be the underlying causes of this protective effect.