Abstract: Three novel tridentate ligands (L¹NH₂ = bis(2-pyridylmethyl)-amino)-ethylamine, L²H = bis(2-pyridylmethyl)-amino)-acetic acid, L³NH₂ = (6-amino-hexyl)-pyridyl-2-methyl-amino-acetic acid) were used as bifunctional chelating agents for the organometallic precursor fac-¹⁸⁸Re (CO)₃(H₂O)₃⁺. The results of labeling condition experiments show that a radiochemical purity higher than 92% can be obtained within 60 min by the reaction of fac-¹⁸⁸Re (CO)₃⁺ core in a condition (pH=7.4) with a very small amount (10^-5mol/L) of these three ligands. The stability experiments in vitro demonstrate that fac-¹⁸⁸Re(CO)₃L¹NH₂⁺, fac-¹⁸⁸Re(CO)₃L²H and fac-¹⁸⁸Re(CO)₃L³NH₂ do not decompose within 24 h (37 ℃, new born calf serum). Biodistributions results indicate that the complexes with tridentate coordinated ligand systems revealed generally a good and fast clearance from all organs and tissues, primarily through the renalurinary pathway with a small portion retained in the hepatobiliary tract. The predominant route of excretion, the urinary tract, seems to correlate with the lg P values found for the complexes. The highest hepatic retention was found for the complex ¹⁸⁸Re(CO)₃L³NH₂ with a lg P value of －0.36. On the basis of these experiments, it appears that functionalization of biomolecules with tridentatechelating ligand systems is feasible for the labeling with fac-¹⁸⁸Re(H₂O)₃(CO)₃⁺ .