Abstract: The invention relates to radiolabelled metallocene derivatives of the general formula ##STR1## wherein Mc is a metallocenyl group with a radioactive central atom,R is a carbonyl or methylene group,R.sub.1 is a hydrogen atom or an alkyl group having 1-4 carbon atoms,A is a carboxy group or a pharmaceutically acceptable salt thereof, or an alkoxycarbonyl or alkanoyl group having 2-5 carbon atoms, andn is 1-4.The invention also relates to radiodiagnostic compositions comprising said radiolabelled metallocene derivatives and to a method of performing a radiodiagnostic examination, in particular of examining the renal function.