Bifunctional chelating molecules linking the fac-Tc-99m(CO)(3)](+) core with targeting biomolecules are required for the development of specific diagnostic radiopharmaceuticals. Diethylenetriamine (1) and N-(pyridin-2-ylmethyl)ethane-1,2-diamine (2) both react readily with (99mT)c(H2O)(3)(CO)(3)](+) in 0.9% saline at micromolar concentrations to form the cationic complexes Tc-99m(1)(CO)(3)](+) (5) and Tc-99m(2)(CO)(3)](+) (6) in quantitative yields. The crystal structures of the corresponding Re or Tc-99 complexes were determined and exhibit in particular the small size of 5. Challenging both Tc-99m complexes 5 and 6 with a 10(4) excess of histidine or cysteine showed no decomposition or ligand exchange after 24 hours and both compounds were also stable against reoxidation to (TcO4)-Tc-99m](-). In normal mice, complex 5 revealed a good and fast clearance from the blood, and most organs. Only limited accumulation in the large intestine was visible after 4 hours. Complex 6 was also excreted relatively quickly from the blood but retention was observed in some tissues after 4 h. In order to illustrate the potential of both ligands to be further functionalized, two derivatives containing potentially DNA binding functionalities, N-(2-Amino-ethyl)-N'-pyren-1-ylmethyl-ethane-1,2-diamine (3) and N-(quinolin-2-ylmethyl)ethane-1,2-diamine (4) were synthesized. The respective Re or Tc-99 complexes were fully characterized. Based on these results, it appears that functionalization of biomolecules with acyclic triamine ligands is biologically relevant. Complex 5 in particular could be used to mimic a terminal amino group in, e. g., a peptide due to its small size and positive charge.