Holmium-166 with its favorable radiation characteristics could be used in endovascular radionuclide therapy (EVRT) technique in liquid filled low-pressure balloon angioplasty. 166Ho-dimethyl di ethylene triamine penta acetic acid (DMDTPA) was prepared and its biodistribution carried out to evaluate its suitability as an EVRT formulation. DMDTPA was synthesized, characterized and was complexed with 166Ho. The complex was stable at 37 degrees C in human serum environment and at room temperature for 48 h. Biodistribution studies in mice revealed rapid renal clearance (approximately 90% of the injected dose in 30 min p.i.) with insignificant retention in any of the major organs including bone. The studies show that 166Ho-DMDTPA is a good formulation which can be explored as an EVRT source.