The growth of atherosclerotic plaques commonly occurs at certain favored sites which have been correlated with local flow conditions. The development of atheroma is influenced by the transport of matter between blood and the wall. The transport and diffusion of cholesterol and proteins increase by increasing the wall shear stress. In order to explain the above facts, a new physical theory has been developed from the standpoint of polymer physics and the theory of rate processes. The principal component of the wall is protein whose macromolecular chains are held together by electrostatic forces and hydrogen bonds in addition to van der Waals forces. The chains are executing thermal segmental motion, by virtue of which cholesterol, or other accumulating material, is transported through protein system as a result of an elementary diffusion jump from one equilibrium position to the next over a potential-energy barrier. When the wall is sheared, weak van der Waals bonds may be broken down to some extent depending upon the magnitude and duration of the shear stress, which results in lowering the potential-energy barrier for diffusing molecules, that is, in increasing its diffusion coefficient.