Electron spectroscopic imaging (ESI) was employed to study, with high spatial resolution, the intracellular distribution of the halogenated derivative of doxorubicin 4'-deoxy-4'-iododoxorubicin (IDX) in sensitive and multidrug resistant human breast carcinoma cells. Both ESI and electron energy loss spectroscopy (EELS) observations confirmed results obtained with flow cytometry (FC), laser scanning confocal microscopy (LSCM) and secondary ion mass spectrometry (SIMS). Moreover, ESI allowed us to obtain a more detailed intracellular localization of IDX. Our results confirm that nuclear DNA represents the main intracellular target for IDX and that the Golgi apparatus is involved in the intracellular transport of the drug.