Abstract: The invention provides materials and methods for the administration of an effectively magnetic medication or diagnostic reagent, or for the removal, sequestration, or effective conversion to a non-deleterious condition of a deleterious substance such as a toxin (e.g., biological, chemical, or radiological compound or composition) in vivo by administering a biocompatible magnetic particle to an organism in need, e.g., by delivery to the bloodstream, with the organism optionally having an internal magnetizable stent or magnetizable seed. The materials and methods are useful in the diagnosis and treatment of a variety of acute and chronic diseases, disorders and conditions afflicting man and other organisms, as well as for the removal of a variety of deleterious substances, including toxins, with the optional aid of an external magnetic generator and an optional magnetic filtration device.