The red blood cell is susceptible to damage by foreign surface interaction and hydrodynamic shear stressing; both of these hemolytic sources are present in blood processing machines which are used to treat chronic and acute disorders. The present investigation attempts to elucidate several facets of the erythrocyte degradation process produced by hydrodynamic shear stress. In this study, a constant shear stress viscometer was used to subject normal human erythrocytes suspended in altered serum environments to known shearing forces. The response of the cells was determined by hemolysis measurements. This study examined 1) the effect of oxygenation on hemolysis, 2) the effect of ATP concentration on hemolysis, and 3) the effects of incubation in various suspending mediums upon erythrocyte characteristics and the relationship between these altered characteristics and cell trauma.