Reverse cholesterol transport (RCT) is the major protective system against atherosclerosis. In this system, cholesteryl ester transfer protein (CETP) is known to facilitate the transfer of neutral lipids between lipoproteins in plasma. We reported the pathophysiological significance of CETP by clinical studies with genetic CETP deficiency, showing that this protein plays a crucial role in the RCT system. However, information about the expression of this protein in the initial step of RCT, macrophages (Mphi) in the blood vessels, is still very limited. In the present study, we have performed immunohistochemical analyses on the expression of CETP in human atherosclerotic lesions. The immunoreactive mass of CETP was abundantly detected in foam cells in human aortic and coronary atherosclerotic lesions, but not in the normal arterial wall. A double immunostaining showed that the majority of CETP-positive foam cells were derived from Mphi and a minor population appeared to derive from smooth muscle cells. Transient transfection of CETP cDNA into COS-7 cells showed that high density lipoprotein (HDL)-mediated efflux of free cholesterol from the cells expressing CETP was much higher than that from mock-transfected cells, while uptake of HDL-lipids was not affected in cells transfected with CETP cDNA. Efflux of free cholesterol from the Mphi obtained from CETP deficiency was significantly decreased compared with that from normal subjects. These data indicate that CETP is expressed in Mphi in the atherosclerotic lesions and may possess an anti-atherogenic function to remove cholesterol from the cells, suggesting another role of CETP at the initial step of RCT.