A new arterial wall permeability function, based on the local wall shear stress gradient, has been developed and employed to simulate enhanced low density lipoprotein transfer across the endothelium. the atherosclerotic model used is that of the aorto-celiac junction of rabbits. The experimentally validated computer simulation model for convection mass transfer provides further evidence that the wall shear stress gradient is a reliable predictor of critical atherogenic sites in branching arteries. Some of the underlying biological aspects of atherogenesis due to locally significant and sustained wall shear stress gradient values are briefly discussed.