Abstract The magnetic structure factor of the equiatomic FeCo alloy has been measured in the disordered phase at 1000 K by polarized neutron diffraction. A comparison with the data collected in the ordered phase at room temperature [E. Di Fabrizio et al., Phys. Rev. B40, 9502 (1989)] shows marked variations that can be ascribed to the thermal motion of nuclei. From the complete set of data vs temperature, the experimental ion-electron linear response function has been deduced and compared to a theoretical Random Phase Approximation model.