The purpose of this study is to reveal the albumin uptake intoendothelial cells in the separated flow area. After 24 hr of exposure toflow induced in a back step flow channel, the endothelial cells wereincubated in 371C for 60 minutes in PBS containingtetramethylrhodamine isothiocyanate conjugated albumin (TRITCalbumin). Thereafter, the cell morphology and the albumin uptakewere observed by a confocal laser scanning microscope (CLSM). In alow shear stress area (stagnant and reattachment areas), the cellsaligned randomly. In a high shear stress area (reversal and fullydeveloped areas), the cells were elongated and aligned to flowdirection. In low-shear-stress and high-shear-stress gradient areas(reattachment areas), the amount of albumin uptake into the cells wasthe largest in all areas. These data indicate that shear stress and shearstress gradient affect the endothelial cell morphology and the albuminuptake into endothelial cells.