The effect of turbulent shear stress on a suspension cell line (KG-1) derived from human erythrocytic leukemia has been studied. The previous studies in the area of shear and animal cells have not been able to provide a quantitative measure of the turbulent shear stress in a stirred bioreactor and correlate the shear forces to the damage of animal cells. The present study bridges that crucial gap and provides a quantitative estimate of the turbulent shear stress existing in the commonly used spinner flask system. The cells were sheared under turbulent conditions by using a magnetic bar at agitation speeds of 2.5, 5 and 7.5 r/s in a spinner flask. The parameters used to estimate cell damage were the total and viable cell count of the population, the proliferating ability and the cytoskeletal structure of the treated cells. The turbulent shear stress experienced by the cells was quantitatively estimated by using a laser Doppler anemometer. The agitation of cells in the presence and absence of fetal bovine serum at a lower agitation speed of 2.5 r/s demonstrated the shear protective effect of serum. The measurement of turbulent stresses in medium with and without serum indicated that serum caused a reduction in the turbulent stresses, thus providing an insight into its protective mechanism.