Abstract: The invention relates to magnetic protein conjugates of the formula IM--NH--CO--(CH.sub.2).sub.n --S--P' Iwith n=1-6, preferably with a n=1 or 2 and particularly preferably with n=1, in which M is a dispersible, magnetically reacting material or particle which carries amino groups, and P' is a protein, to a process for the preparation thereof and to the use thereof for the specific removal of cells or soluble antigens, receptors, substrates, cofactors or carbohydrate determinants from aqueous salt solutions or body fluids or as part of a diagnostic method or as a diagnostic aid, preferably for the removal of cells, preferably for bone marrow depletion or for HLA typing.