Abstract 5-Iminodaunorubicin is an anthracycline derivative exhibiting promising antitumor activity. Using potentiometric and spectroscopic measurements we have shown that 5-iminodaunorubicin forms with Fe(III) a complex in which three molecules of drug are bound to one Fe(III) ion. Each molecule is chelated through the C-12-carbonyl and the C-11-phenolate oxygen atoms. The stability constant is 1.6 · 10 34. Using circular dichroism measurements we have studied the interactions of 5-iminodaunorubicin with cardiolipin-containing vesicles. We have shown that cardiolipin could bind one molecule of drug without penetration of the dihydroanthraquinone moiety into the bilayer.