Immunological materials

A cytotoxic agent comprising an immunoglobulin specific for antigens on the surface of cells to be killed having 1-10 polymer carrier molecules convalently bound thereto, said polymer carrier having about 5-500 molecules of a cytotoxic drug covalently bound thereto and said polymer carrier having a molecular weight of 5000-500,000 and free carboxyl, amino or cycloimidocarbonate groups for covalently bonding, said cytotoxic drug also having amino or carboxyl groups available for covalent bonding.