Transition metal complexes with terpyridine ligands have attracted a widespread interest with respect to biomedical applications: [(tpy)PtCl]Cl and [(tpy)RuCl(3)] are potent anti-tumor agents with activities comparable to those of cisplatin and carboplatin. The Ru(II) complexes feature a high potential as reactive probes for DNA oxidation; whereas, luminescent Ir(III), Pt(II) or Eu(III) complexes have been utilized in biolabeling applications. Besides complexes based on heavy second or third row transition metal ions, remarkable results have been obtained with respect to the development of new types of metallodrugs, based on the naturally more abundant and intrinsically less toxic first row transition metal ions (e.g. Fe(II), Cu(I/II), Zn(II)). The perspective of these complexes in particular with respect to future biomedical applications in chemotherapy and cleavage of nucleic acids is evaluated in this review.