To substantiate our hypothesis that concentration polarization of low-density lipoprotein (LDL) plays an important role in the localization of atherogenesis, we investigated the effects of wall shear stress and water filtration rate (or perfusion pressure) on the luminal surface LDL concentration (c(w)) and the LDL uptake by human vascular endothelial cells and smooth muscle cells co-cultured on a permeable membrane using a parallel-plate flow chamber technique and a flow cytometry method. The results indicated that the uptake of fluorescent labeled LDL (DiI-LDL) by the co-cultured cells was positively correlated with c(w) in a non-linear fashion. When c(w) was low, the uptake increased very sharply with increasing c(w). Then the increase became gradual and the uptake was seemingly leveled out when c(w) reached beyond 160 microg/ml. The present study therefore has provided further experimental evidence that concentration polarization may occur in the arterial system and have a positive correlation with the uptake of LDLs by the arterial wall, which gives support to our hypothesis regarding the localization of atherogenesis.