To test whether the macrophages in vein grafts may invade into the vascular wall from the adventitia apart from the lumen.Expression of CD68 (a marker of macrophage) and CD31 (a marker of endothelial cells) in 30 vein grafts were detected by confocal immunofluroscence. Images were processed with Silicon Graphics Octane.In normal veins, there were a few CD68 positive cells in the adventitia, but few CD68 positive cells were found in the media and the intima. In the diseased vein, CD68 positive cells were significantly increased and present in all layers of the vascular wall, the adventitia, media and intima, extending from the adventitia to the media. There was a close relationship between the penetration of CD68 positive cells into the media from the adventitia and the angiogenesis in the media.The adventitia may be an important pathway for macrophage invasion.