Particles (I) for use in diagnosis and therapy, especially for binding with an active therapeutic agent, have a nanocrystalline magnetic core and an envelope enclosing the core. The core comprises at least 95 wt.% iron oxide and the specific saturation magnetization of the particle is at least 110 Am 2>；/kg iron. Independent claims are also included for the following: (A) medicament or diagnostic agent containing (I)； (B) preparation of magnetic particles for use in diagosis and therapy, particularly (I)； (C) use of (I) for the manufacture of a medicament or in diagnosis, where (I) are bound to an active agent or a diagnostic agent, respectively. ACTIVITY : Cytostatic； Antibacterial； Antirheumatic； Anticonvulsant； Gynecological； Osteopathic； Vasotropic； Thrombolytic； Neuroprotective； Auditory； MECHANISM OF ACTION : None given.
