We investigated whether platelet activation can be correlated with angiographic severity and the degree of collateralization in coronary artery disease (CAD), as well as endothelial damage/dysfunction. No studies have attempted to correlate platelet activation status, as measured by soluble plasma markers (soluble CD40 ligand, soluble P-selectin, soluble glycoprotein V), with the appearance of diseased coronary arteries. We found evidence of increased platelet activation in CAD, but a lack of correlation between the degree of platelet activation and the angiographic disease severity, which may reflect the presence of disease elsewhere or the presence of coronary atheroma not detected by angiography.