Abstract: An initial aqueous pertechnetate solution which has a low electrolyte concentration compared with physiological saline is treated by passage through a bed of insoluble ion exchange material for adsorbing the pertechnetate. In a second step an ionic eluant having a smaller volume than the pertechnetate solution is passed through the bed to remove the pertechnetate to provide a relatively concentrated and pure eluate solution, the ion exchange material in the bed and the ionic eluant having respective properties for providing the eluate with a pH suitable for radiopharmaceutical purposes. The bed retains thereon radionuclidic impurities which may have been in the initial solution. The method can be valuable for treating the eluate from a portable technetium generator which is eluted with water and advantageously the insoluble material in the bed is zirconium oxide.