Objectives: Heat shock proteins (HSP) belong to a family of proteins expressed in times of cellular injury which prevent enzymatic denaturation and ultimately apoptosis. We hypothesized that there would be expression of two HSP 60 and 70, incited by endothelial damage that accompanies atherosclerotic disease. In addition, we sought to determine if there was a quantitative difference in the level of expression between ulcerated and non-ulcerated plaques. Methods: Twenty-one carotid plaque specimens were obtained from patients undergoing carotid endarterectomies. All plaques were removed intact with the intima undisturbed, using the eversion technique. Ulceration was determined via angiography and the plaques were further subdivided into ulcerated (sixteen) and non-ulcerated (five). Normal cultured human aortic endothelial cells served as controls. The plaques were placed in formalin, immunostained with monoclonal antibodies to HSP 60&70 and then analyzed via digital image analysis to quantify HSP 60&70 expression. The intensity staining index (ISI) was determined and statistical significance was determined using a student T-test with a 95% confidence interval. Results: HSP 70 expression was greatly enhanced in the carotid plaques (ISI = 150), when compared to non-atherosclerotic aortic endothelial cells (ISI = .02). Conclusions: Atherosclerotic carotid arteries have high levels of apoptosis as shown by other investigators. We have shown that carotid lesions express an increase in HSP 70, which has a direct inhibitory effect on apoptotic stimuli. The increased levels of HSP 60 & 70 expression in non-ulcerated plaques suggests that these proteins retard the apoptotic stimuli ultimately, retarding the degradation and instability of ulcerated arterial lesions. TABLE—ABSTRACT P75Ulcerated ISINon-ulcerated ISIP-valueHSP 609.6245.31.02HSP 70119182.05