Abstract: A complex of a chelating agent is formed and labelled with technetium-99m. The chelating agent is either an ethylenediamine carboxylic acid or its salt having a phenolic group at each end of the molecule such as EDDHA and HBED or alternatively the phenolic amino carboxylic acid or its salt having a single phenolate group such as HBG or HBS. The complex is a stannous complex which when labelled with technetium-99m has a good balance of lipo-solubility and waater-solubility to permit hepato-biliary imaging. The radiopharmaceutical may be useful for assessing hepatobiliary function in animals including human beings. A particularly useful chelating agent is ethylene-bis-(.alpha.-imino-2-hydroxy-5-bromophenyl acetic acid).