[en] The cross-section of the ²³⁹Pu (n,2n)²³⁸Pu reaction is relatively well-known between 8 and 12 MeV for incident neutron energy but different models disagree between 6 and 8 MeV as well as beyond 12 MeV. A new measurement method has been developed, this method is based on the recovery of the quantity of Pu²³⁸ produced by the reaction during a few hundreds hours of irradiation and at an energy of 6.88 MeV for the incident neutron. The result confirms the disagreement between the JEFF3.3 evaluation and previous data. One of the issues of this method is to determine the right efficiency of the recovery of the quantity of Pu²³⁸. Another issue was to get a quantity of ²³⁹Pu pure enough as the experiment has shown that some Pu²³⁸ initially present in the Pu²³⁹ target was recovered as reaction product. (A.C.)