To elucidate that in iron-catalyzed oxidative damage the interaction of iron complex with the target molecules is important, the oxidative damage to plasmid DNA, protein and fatty acid has been compared using iron-chelate complexes with nitrilotriacetic acid (nta), citric acid, ethylenediamine-N,N'-diacetic acid (edda) and diethylenetriamine-N,N,N',N",N"-pentaacetic acid (dtpa). In the presence of hydrogen peroxide, plasmid pBR322 strand breaks occurred in the order of Fe-edda > Fe-citrate > Fe-nta > > Fe-dtpa. However, fragmentation of bovine serum albumin and diene conjugation of linoleic acid micelle occurred in the order of Fe-nta > Fe-edda > > Fe-citrate > Fe-dtpa = O, which were similar to hydroxyl radical production by these iron complexes and H2O2. Bleomycin-detectable free radical-promoting irons in these iron complexes were about 85% of iron in Fe-nta, Fe-citrate and Fe-edda, and only about 33% in Fe-dtpa. Not only hydroxyl radical productivity and free radical-promoting iron content in iron complex, but also the interaction of the complex with the target molecules determines the iron-catalyzed oxidative damage.