Abstract-The phylogenetically conserved nature of heat shock proteins (Hsp) has led to the proposition that they may provide a link between infection and the inflammatory component to vascular disease. Hypertension is associated with atherosclerosis. Here, we measured circulating heat shock protein and heat shock protein antibody levels in association with borderline hypertension. Seventy-two men with borderline hypertension patients and 75 normotensive control subjects (diastolic blood pressure 85 to 94 and Ͻ80 mm Hg, respectively) were selected from a population-screening program. The levels of Hsp60; Hsp70; and anti-human Hsp60, anti-human Hsp70, and anti-mycobacterial Hsp65 antibodies were determined with enzyme immunoassay. The presence of carotid atherosclerosis and the intima-media thickness values were determined with ultrasonography. A major novel observation in this report was the detection of circulating Hsp60, which was present at a significantly enhanced level in patients with borderline hypertension. Furthermore, serum Hsp60 was associated with intima-media thicknesses (PϽ0.01). Anti-Hsp65 antibody levels were higher in borderline hypertension (PϽ0.001), whereas Hsp70 and anti-Hsp70 antibody levels did not differ. In contrast to anti-Hsp65 antibody, anti-Hsp60 antibody levels were lower in borderline hypertension (PϽ0.03), although the difference was quantitatively small. None of the parameters evaluated were associated with atherosclerosis, metabolic factors, or smoking. We identified elevated Hsp60 levels in patients with borderline hypertension and an association between early atherosclerosis and Hsp60 levels. The physiological role of Hsp60 release has yet to be defined, but given the proinflammatory properties, these proteins could be involved in the induction/progression of both hypertension and atherosclerosis, as well as being markers for early cardiovascular disease. (Hypertension. 2000;36:303-307.)