This study examined the cytotoxic effects of the gamma-Fe2O3 magnetic nanoparticles (GMNs) on a range of tumor cell lines. GMNs, approximately 20 nm in diameter, were prepared using a chemical coprecipitation technique, and coated with two surfactants to obtain a water-based product. A 3-(4, 5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide assay revealed the GMNs to be non-toxic to human fibroblast cells and most of the tumor cell lines tested. However, the magnetic nanoparticles coated with the anti-cancer drugs exhibited cytotoxic activity against tumor cells. These results suggest that GMNs are not cytotoxic to the tumor cells and normal human cells tested in this study. In addition, the magnetic nanoparticles are biostable and magnetic nanoparticles coated with anti-cancer drugs are effective drug delivery vehicles. These results highlight the potential of drug-coated Fe2O3 magnetic nanoparticles as new anti-tumor agents. (C) 2010 Elsevier B.V. All rights reserved.