the present invention relates to a highly efficient method of preparing modified microcapsules exhibiting selective targeting . these microcapsules are suitable for encapsulation surface attachment of therapeutic and diagnostic agents . in one aspect of the invention , surface charge of the polymeric material is altered by conjugation of an amino acid ester to the providing improved targeting of encapsulated agents to specific tissue cells . examples include encapsulation of radiodiagnostic agents in 1 μm capsules to provide improved opacification and encapsulation of cytotoxic agents in 100 μm capsules for chemoembolization procedures . the microcapsules are suitable for attachment of a wide range of targeting agents , including antibodies , steroids and drugs , which may be attached to the microcapsule polymer before or after formation of suitably sized microcapsules . the invention also includes microcapsules surface modified with hydroxyl groups . various agents such as estrone may be attached to the microcapsules and effectively targeted to selected organs .