Production of technetium-labelled complexes

A process for making a complex of Tc-99m with a dimercapto aliphatic compound is claimed. The compound has from 2 to 15 carbon atoms and contains a total of from 1 to 5 water-solubilizing substituents of the class consisting of hydroxyl, carboxylic or sulfonic groups, and at least one water-solubilizing substituent for every 3 carbon atoms but not more than 3 carboxylic or one sulfonic group. The compound is water-soluble and stable at pH 7.4. The complex has a partition coefficient in water-octanol with ln(asub(w)/asub(o))>=2, where asub(w) is the radioactivity distributed in the aqueous phase and asub(o) is the radioactivity distributed in the organic phase at a ph in the range 4 to 9. This coefficient does not change more than three units over this range