<Fluid-mechanical damages> of <shear sensitive> animal cells due to forces generated by media agitation and aeration are reviewed. In anchorage-dependent cultures grown in a stirred bioreactor the cell damage is caused by small turbulent eddies of size of the microcarrier beads and by collision between <microcarriers> and against the impeller and the stationary parts of bioreactor. In the freely suspended cells grown in stirred or <air-lift reactor>s the cell damage is due mainly to air bibble breakup. The mechanical damages can be limited by an increase of kinematic viscosity of fluid and reduction to the local energy dissipation rate. Biological aspects of shear stress are also discussed.