Fine magnetite nanoparticles, both electrostatically stabilized and nonstabilized, were synthesized in situ by precipitation of Fe(II) and Fe(III) salts in alkaline medium. Magnetic poly(glycidyl methacrylate) (PGMA) microspheres with core-shell structure, where Fe3O4 is the magnetic core and PGMA is the shell, were obtained by dispersion polymerization initiated with 2,2'-azobisisobutyronitrile (AIBN), 4,4'-azobis(4-cyanovaleric acid) (ACVA), or ammonium persulfate (APS) in ethanol containing poly(vinylpyrrolidone) or ethylcellulose stabilizer in the presence of iron oxide ferrofluid. The average microsphere size ranged from 100 nm to 2 mum. The effects of the nature of ferrofluid, polymerization temperature, monomer, initiator, and stabilizer concentration on the PGMA particle size and polydispersity were studied. The particles contained 2-24 wt % of iron. AIBN produced larger microspheres than APS or ACVA. Polymers encapsulating electrostatically stabilized iron oxide particles contained lower amounts of oxirane groups compared with those obtained with untreated ferrofluid. (C) 2004 Wiley Periodicals, Inc.