Raman spectroscopy offers a powerful new way to look at atherosclerotic tissue. Rather than categorizing disease in terms of arterial luminal diameter reduction, Raman spectroscopy allows a qualitative and quantitative biochemical description of the diseased vascular segment. The clinical implications are enormous, inasmuch as plaque composition rather than plaque volume appears to be the most important predictor of clinical outcome. Knowledge of plaque composition is likely to improve the physician's ability to predict plaque behavior, and it may also provide a means to monitor the effects of medical interventions.