Novel radioactive estradienes labelled with iodine of the formula ##STR1## in the form of their syn or anti isomers or mixtures thereof wherein the wavy line indicates anti or syn position, R is selected from the group consisting of hydrogen, alkyl of 1 to 6 carbon atoms and acyl of an organic carboxylic acid of 1 to 12 carbon atoms and R.sub.1 is the residue of an amino acid R.sub.1 NH.sub.2 possessing an iodine acceptor group or a derivative thereof labelled with iodine .sup.125 or .sup.131 and their preparation and novel intermediates, antigens prepared from the compounds of formula I and bovine seric albumin or human seric albumin and their preparation and their use for the preparation of antibodies.