Abstract A key issue in the long-term programme of European Fusion Development Agreement (EFDA) is the experimental validation of the neutron-induced activation predicted by calculations for structural materials developed for fusion application. Up to now, experiments have been carried out at neutron generators producing mono-energetic 14 MeV neutrons and using experimental assemblies simulating reactor-like neutron flux spectra. Since in October 2003 a Tritium Trace Experiment (TTE) was performed at JET, two samples of EUROFER-97 were exposed to the real DT neutron source produced in the tokamak. The goal was to measure the activity induced by neutrons in this material and to compare it to that calculated using the European Activation System EASY-2003 with FENDL-2/A neutron activation cross-section library. This was the first attempt to compare experimental data obtained in a real DT neutron spectrum with calculation results. The conclusion of this work is that the EASY code and the FENDL-2/A can evaluate the induced activity of medium half-life isotopes with an acceptable uncertainty, within the experimental total error.