polymeric functional microspheres containing metal or metal compounds are formed by addition polymerization of a covalently bondable olefinic monomer such as hydroxyethylmethacrylate in the presence of finely divided metal or metal oxide particles , such as iron , gold , platinum or magnetite , which are embedded in the resulting microspheres . the microspheres can be covalently bonded to chemotherapeutic agents , antibodies , or other proteins providing a means for labeling or separating labeled cells . labeled cells or microspheres can be concentrated at a specific body location such as in the vicinity of a malignant tumor by applying a magnetic field to the location and then introducing the magnetically attractable microspheres or cells into the circulatory system of the subject . labeled cells can be separated from a cell mixture by applying a predetermined magnetic field to a tube in which the mixture is flowing . after collection of the labeled cells , the magnetic field is discontinued and the labeled sub - cell population recovered .