In May 1999 the 7th meeting of the "Comité Consultatif pour la Masse et les Grandeurs Apparentées" (CCM) came to the decision to perform an international key comparison CCM.M-K3. It was agreed that the participating laboratories carry out a mass determination of a 50 kg standard weight with the smallest possible measurement uncertainty. The BNM-LNE (France) had the function of the pilot laboratory and was supported by the NRC (Canada) and the PTB. 14 institutes took part in the comparison. The differences between the results of the individual institutes and the reference value (median) are for all participants within the given expanded measurement uncertainties (k = 2). The result of the PTB differs with the smallest of all measurement uncertainties (3,3 mg) by only 2,2 mg from the reference value.