An understanding of hydrodynamic shearing of biological cells provides basic information about the mechanical properties of cells, their deformations occurring in natural circulations and is necessary for effective design of artificial circulation devices. Several situations including (i) shearing in cone-plate viscometers, (ii) forced flow through tubes and hypodermic needles, as well as (iii) acoustic microstreaming near oscillating bubbles and wires provide controlled shearing. Details of the deformation and disruptions of cells in shear fields are understood by considerations of theory describing emulsification processes. Viscoelastic parameters of the erythrocyte can be obtained using a model based upon the dynamic behavior of polysutfide rubber.