A nontoxic drug nanocarrier containing carboxyl groups was successfully developed by mixing magnetic nanoparticles (MNPs) of Fe(3)O(4) with the water-soluble polyaniline derivative poly[aniline-co-sodium N-(1-one-butyric acid) aniline] (SPAnNa) and doping with HCl aqueous solution to form SPAnH/MNPs shell/core. SPAnH/MNPs could be used to effectively immobilize the hydrophobic drug paclitaxel (PTX), thus enhancing the drug's thermal stability and water solubility. Up to 302.75 mug of PTX could be immobilized per mg of SPAnH/MNPs. SPAnH/MNPs-bound-PTX (bound-PTX) was more stable than free-PTX at both 25 degrees C and 37 degrees C. Furthermore, bound-PTX was more cytotoxic to human prostate carcinoma cells (PC3 and CWR22R) than free-PTX at 37 degrees C, and the inhibition of cellular growth was even more pronounced when magnetic targeting was applied to the bound-PTX. These data indicate that this magnetically targeted drug delivery system provides more effective treatment of prostate cancer cells using lower therapeutic doses and thus with potentially fewer side-effects.