Anchimeric chelating compounds which are capable of rapidly forming stable chelates with radionuclide metals at or below physiological temperatures are disclosed. The compounds possess a first site capable of complexing with a radionuclide metal which can be transferred to a second site (to form a chelate) by incubation, such as at 37°C or below. These anchimeric chelating compounds may be bifunctional and so are useful for radiolabelling target specific molecules such as monoclonal antibodies and fragments thereof, that may be specific for cancer cells.