A comprehensive study of the technique of High Gradient Magnetic Separation applied to erythrocytes is described. Experiments indicate that magnetic filters are capable of removing in excess of 95% of erythrocytes from an input suspension within a few minutes. Studies of the interaction of a single erythrocyte with a single wire have been carried out. This work involved the development of a novel phase gradient optical system. When used in conjunction with a new design of experimental flow cell this enabled both single wire capture and erythrocyte buildup to be studied. Analysis of erythrocyte trajectories in the axial configuration confirm the magnetostatic theory used. Data from both the axial and transverse configurations indicate that a laminar flow model provides a better description of the hydrodynamic forces than the commonly used potential flow model. The shapes of the erythrocyte deposit on a single wire in the axial, transverse and longitudinal configurations are consistent with the predictions of the magnetostatic analysis. Extension of the single wire analysis to the prediction of the absorption coefficient of a filter indicates that wire-wire interactions require further study. However, it does provide a basis for predicting the dependence of the absorption coefficient on parameters such as the fluid flow rate and the wire characteristics. Cell viability studies indicate that erythrocytes, neutrophils and platelets are not adversely affected by the separation process.