Metal complexes continue to attract considerable attention for applications in the chemotherapy of a variety of diseases. In this lecture we will provide an overview of our work on ruthenium complexes of potential chemotherapeutic value, making use of the concept of metal-drug synergism. Coordination of ruthenium-containing fragments to organic drugs like clotrimazole or ketoconazole resulted in enhanced biological activity against Trypanosoma cruzi, the causative agent of Chagas disease, by a dual mechanism of action involving inhibition of sterol biosynthesis and DNA binding; the same compounds were also active against some types of tumors by a mechanism different from that of cisplatin. Also, we have synthesized ruthenium complexes containing chloroquine as a ligand, which display activity against malaria parasites, in some cases against resistant strains. Mechanistic studies indicate that the main target is heme aggregation and that the lipophilicity of the compounds plays a key role in the activity and the lowering of resistance.