Abstract: The invention relates to magnetically targetable particles comprising at least one magnetic component The particles are capable of delivering selectively to a site or organ a biologically active substance for in vivo medical diagnosis and/or treatment. The particles are prepared by many processes such as encapsulation processes. Also described are methods for making the particles, methods for localized in vivo delivery of a biologically active agent utilizing the particles, a kit for the administration of the particles, as well as a method for sterilizing the particles.