In this article we briefly describe our recent results concerning the interaction of mononuclear [M(CO)3]+ (M = Re, 99Tc and 99mTc) based complexes with guanine and plasmid DNA for chemo- and/or radiotherapeutic purposes. Furthermore, studies with mono- and dinuclear, coordinatively unsaturated Ni(II) and Cu(II) complexes inducing B- to Z-DNA transitions are outlined. The strong interaction of [M(CO)3]+ with one guanine allows the direct introduction of this core into oligodeoxynucleotides (ODN), without their previous derivatization, for further elucidation of their biological behavior. Vectors labeled in this way can later be used in radioimaging or -therapy studies. The [M(CO)3]+ core can also mediate the introduction of further biologically active or, for analytical purposes, fluorescent molecules. Alternatively, ODNs can be derivatized with amino acid based chelators such as histidine. We describe the induction of structural changes in plasmid DNA observed after reaction with the [M(CO)3]+ moiety. This indicates a cisplatin-like behavior useful for future chemotherapy. Finally, studies of the interaction of mono- and dinuclear complexes with ODN inducing B- to Z-DNA transitions are described and compared to the effect of common electrolytes alone. A clear correlation between salt type and salt concentration was found. These complexes have a strong potential to be used for analytical or biological purposes as well.