[en] Technetium-99m MDP was prepared from MDP kits from several different sources. The resulting [/sup 99m/Tc]MDP preparations were analyzed by electrophoresis. The results demonstrated the presence of at least four different /sup 99m/Tc complexes in these preparations. Modified kit preparations were analyzed to show the effects of concentration and pH on formation of the impurities. The electrophoresis results were correlated with scintillation camera imaging studies in rabbits and suggest that hydrolysis of MDP to phosphate and methylphosphate results in formation of /sup 99m/Tc complexes with poor biological behavior as bone scanning agents