The study investigates the effects of hemodynamic forces on vascular endothelial cell turnover in vitro. Confluent cell monolayers of bovine aortic endothelial cells were exposed to varying levels of laminar and turbulent shear stresses. Laminar shear stresses (8-15 dynes/cm²) induced cell alignment without initiating the cell cycle, while turbulent shear stresses as low as 1.5 dynes/cm² for 3 hours stimulated substantial endothelial DNA synthesis without cell alignment, discernible cell retraction, or cell loss. The results suggest that in atherosclerotic lesion-prone regions, unsteady blood flow characteristics, rather than the magnitude of wall shear stress, may be the primary determinant of endothelial cell turnover. The study highlights the sensitivity of endothelial cells to turbulent flow characteristics, even at very low shear stress levels, and postulates that small-scale, high-frequency fluctuations in turbulent shear stress may be crucial for initiating cell turnover.The study investigates the effects of hemodynamic forces on vascular endothelial cell turnover in vitro. Confluent cell monolayers of bovine aortic endothelial cells were exposed to varying levels of laminar and turbulent shear stresses. Laminar shear stresses (8-15 dynes/cm²) induced cell alignment without initiating the cell cycle, while turbulent shear stresses as low as 1.5 dynes/cm² for 3 hours stimulated substantial endothelial DNA synthesis without cell alignment, discernible cell retraction, or cell loss. The results suggest that in atherosclerotic lesion-prone regions, unsteady blood flow characteristics, rather than the magnitude of wall shear stress, may be the primary determinant of endothelial cell turnover. The study highlights the sensitivity of endothelial cells to turbulent flow characteristics, even at very low shear stress levels, and postulates that small-scale, high-frequency fluctuations in turbulent shear stress may be crucial for initiating cell turnover.