The formation of atherosclerotic plaques as a consequence of lipid accumulation in arterial walls apperently is not only caused by a complete removal of endothelial cells of the intima but is also observable under intact endothel. The active storage process of lipids is based on hitherto only insufficiently understood molecular mechanisms where oxidative modifications of LDL and macrophages play a pivotal role for the formation of so called, 'foam cells' - a characteristic feature of atherosclerotic lesions. The article tries to describe initial steps of the foam cell formation. It characterizes the pathophysiological importance of oxidative modified LDL and macrophages in atherogenesis. Further on it reports about pathogenetic relevant criteria for the course of oxidative modifications at LDL components and their consequences which encloses the emigration of monocytes in the cellular network of the arterial wall and the internalisation of oxidative modified LDL in macrophages.