Early non-invasive diagnostic information would be useful in identifying patients at risk of progressive carotid atherosclerosis, despite an apparently harmless plaque on ultrasound imaging. In this study, we assessed the possible association of intracellular cytokines in peripheral blood with the ultrasound (stenosis > or = 70%) and clinical indications (transient ischaemic attack, amaurosis fugax or stroke) for carotid endarterectomy (CEA) in patients. Intracellular cytokine expression was determined in 106 patients (67 undergoing and 39 not undergoing CEA). Cells primed for the proinflammatory cytokines tumour necrosis factor (TNF)-alpha, interferon (IFN)-gamma, interleukin (IL)-1beta, IL-6, IL-8 and the anti-inflammatory cytokines IL-4 and IL-10 were found in significantly higher percentages in patients undergoing CEA than in patients who were not (P < 0.05). Intracellular cytokine expression was significantly higher in patients undergoing CEA who had stenosis > or = 70% (TNF-alpha, IFN-gamma, IL-1beta, IL-6, IL-4 and IL-10), with previous stroke (IFN-gamma, IL-1beta, IL-6, IL-8, IL-4 and IL-10) and with amaurosis fugax (IFN-gamma, IL-6, IL-4 and IL-10) than in patients not undergoing CEA. Increased intracellular cytokines in patients' peripheral blood might be a warning signal indicating progressive atherosclerosis. If so, intracellular cytokine monitoring could help in selecting patients at high risk of future clinical cardiovascular events and therefore most likely to benefit from CEA or adjustment of pharmacological therapy.