The design of clinically useful iron chelators requires attention to be paid to 3 key parameters: oral absorption, selectivity and affinity for iron(III) and toxicity. Factors which influence these 3 parameters are discussed. Hydroxypyridinones are identified as key ligands and properties leading to minimal toxicity and optimum distribution for the treatment of thalassaemia are presented. Key metalloenzymes which are inhibited by iron chelators are identified.