Metallocenes and metallocene derivatives having a radioactive central atom

A process for the production of metallocenes or metallocene derivatives with a radioactive central atom, which comprises heating at 150.degree.-200.degree. C. for 0.1-3 hours a non-radioactive metallocene or metallocene bearing a substituent selected from the group consisting of --COOH, --COO-alkyl, CONH.sub.2, alkanoyl, halogen, amino or dialkylamino wherein alkyl and alkanoyl in each instance are of 1-8 carbon atoms on at least one cyclopentadienyl radical, with a radioactive metal nuclide selected from Group VIII and Subgroups VI and VII of the Periodic Table which is capable for forming a metallocene in ionic form and thereafter separating the thus-obtained radioactive metallocene or metallocene derivative from the ionic radioactive starting material.