Since 1976, ten national metrology institutes (NMI) and another laboratory have submitted 21 samples of known activity of Fe-59 to the International Reference System (SIR) for activity comparison at the Bureau International des Poids et Mesures. The activities ranged from about 200 kBq to 20 MBq. The degrees of equivalence between each equivalent activity measured in the SIR and the key comparison reference value (KCRV) have been calculated and the results are given in the form of a matrix for ten NMI. A graphical presentation is also given.