Turbulent fluid shear stress induces vascular endothelial cell turnover in vitro. This study investigated the effects of hemodynamic forces on vascular endothelial cell turnover by exposing contact-inhibited confluent cell monolayers to shear stresses in laminar or turbulent flow. 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, retraction, or loss. These findings suggest that unsteady blood flow characteristics, rather than the magnitude of wall shear stress, may be the major determinant of hemodynamically induced endothelial cell turnover in atherosclerosis-prone regions. Hemodynamic forces are implicated in the initiation, localization, and development of atherosclerosis. The endothelial cell lining of blood vessels is essential for normal vascular function, and flow characteristics in certain areas of the aorta and its branches are variable and complex. In regions such as the descending thoracic aorta and distal carotid arteries, pulsatile laminar flow is prevalent, while in other regions, such as coronary arteries and the carotid bifurcation, secondary flows, vortices, and intermittently changing flow directions are encountered. The distribution of atherosclerotic lesions is closely correlated with disturbed flow in major vessels. The study used a modified cone-plate viscometer to expose bovine aortic endothelial cells to laminar or turbulent flow. Exposure to laminar flow at 8 dynes/cm² caused cell alignment, while turbulent flow at 1.5 dynes/cm² resulted in random cell orientation and increased DNA synthesis. Prolonged exposure to turbulent flow led to cell retraction and loss. Endothelial cell turnover was significantly increased in turbulent flow compared to laminar flow, with short exposure to low shear stress stimulating DNA synthesis without cell retraction. The results suggest that turbulent flow characteristics, rather than the magnitude of shear stress, are more important in inducing endothelial cell turnover. The study highlights the sensitivity of endothelial cells to turbulent flow and the potential role of unsteady flow patterns in atherogenesis.Turbulent fluid shear stress induces vascular endothelial cell turnover in vitro. This study investigated the effects of hemodynamic forces on vascular endothelial cell turnover by exposing contact-inhibited confluent cell monolayers to shear stresses in laminar or turbulent flow. 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, retraction, or loss. These findings suggest that unsteady blood flow characteristics, rather than the magnitude of wall shear stress, may be the major determinant of hemodynamically induced endothelial cell turnover in atherosclerosis-prone regions. Hemodynamic forces are implicated in the initiation, localization, and development of atherosclerosis. The endothelial cell lining of blood vessels is essential for normal vascular function, and flow characteristics in certain areas of the aorta and its branches are variable and complex. In regions such as the descending thoracic aorta and distal carotid arteries, pulsatile laminar flow is prevalent, while in other regions, such as coronary arteries and the carotid bifurcation, secondary flows, vortices, and intermittently changing flow directions are encountered. The distribution of atherosclerotic lesions is closely correlated with disturbed flow in major vessels. The study used a modified cone-plate viscometer to expose bovine aortic endothelial cells to laminar or turbulent flow. Exposure to laminar flow at 8 dynes/cm² caused cell alignment, while turbulent flow at 1.5 dynes/cm² resulted in random cell orientation and increased DNA synthesis. Prolonged exposure to turbulent flow led to cell retraction and loss. Endothelial cell turnover was significantly increased in turbulent flow compared to laminar flow, with short exposure to low shear stress stimulating DNA synthesis without cell retraction. The results suggest that turbulent flow characteristics, rather than the magnitude of shear stress, are more important in inducing endothelial cell turnover. The study highlights the sensitivity of endothelial cells to turbulent flow and the potential role of unsteady flow patterns in atherogenesis.