The objectives of this year's research were to develop a method for rapidly determining TcO4− in 99Mo//sup 99m/Tc generator eluates, to improve the ability to chromatographically determine individual Tc-HEDP complexes in radiopharmaceuticals, and to investigate the effects of TcO4− concentration and electrochemical reduction on the types and relative amounts of Tc-HEDP complexes present in a radiopharmaceutical formulation. A rapid and sensitive high performance liquid chromatographic (HPLC) method for the quantitative determination of pertechnetate (TcO4−) was developed. This HPLC-based analysis may be of considerable utility in assessing the history and function of 99MO/sup 99m/Tc generators as well as in the routine analysis of reduced technetium radiopharmaceuticals for the presence of undesired TcO4−. Encouraging results were obtained on a dimethyl amine column using aqueous (NH4)2SO4 as the mobile phase. The preparation of Tc(NaBH4) HEDP radiopharmaceutical analogues using varying concentrations of total TcO4− shows a dramatic effect in the number and distribution of Tc-HEDP complexes over a TcO4− concentration range of 10−2 to 10−8M. These results suggest that total TcO4− concentration is an important parameter to be considered in the preparation of a specific Tc-HEDP complex to improve skeletal imaging. The preparation of Tc(electrode) HEDP radiopharmaceutical analogues by using electrochemical reduction was explored. The resulting solutions contain Tc-HEDP complexes that are tentatively identified as being the same complexes formed by NaBH4 reduction, although the relative concentrations of these complexes are quite different with the two modes of reduction. Thus, electrochemical reduction shows promise as a viable route to the preparation of specific Tc-HEDP complexes for improved skeletal imaging.