Xanthoma and atherosclerosis are similar in having infiltrations of macrophages that have transformed into foam cells. The oxidized low-density lipoprotein (LDL) promotes adhesion of monocytes to endothelial cells by inducing expression of adhesion molecules on vascular endothelial cells. Macrophages transform into foam cells by incorporating oxidized LDL using several kinds of scavenger receptors. Very recently, it has been shown that LDL oxidation occurs within lysosomes in macrophages in atherosclerotic lesions and the increase of intra-lysosomal PH can prevent LDL oxidation. Given that proton pump inhibitors can decrease the intra-lysosomal acidicty through inhibition of the lysosomal membrane H+/K+ATPase, theses agents could afford protection against atherosclerosis and xanthoma formation.