Monodisperse colloidal spheres of Pb embedded with superparamagnetic Fe3O4 nanoparticles have been synthesized by refluxing lead acetate in the presence of a magnetite-based ferrofluid in tetra(ethylene glycol), followed by quenching with cold ethanol. Depending on the amounts of ferrofluid and lead acetate fed to the reaction mixture, the molar ratio of encapsulated Fe3O4 to Pb could be varied in the range of 0.001-0.06. Both superparamagnetic and superconducting properties were characterized by SQUID measurements. These results demonstrate a simple, solution-phase approach to the controlled synthesis of composite colloidal spheres displaying a combination of superconducting and superparamagnetic properties. (c) 2007 Elsevier B.V. All rights reserved.