[en] Measurements of the (α,2α) reaction in the GeV region on ¹⁶O and ²⁸Si are described. The results are compared with a calculation employing the plane wave impulse approximation (PWIA) and with a calculation employing the distorted wave impulse approximation (DWIA). The PWIA calculation reproduces the shape of the angular distribution of the observed quasi-elastic events. The main effect of the distortion introduced in the DWIA calculation is to attenuate the quasi-elastic cross section by a factor of five. As a consequence, the (α,2α) reaction in the GeV region is expected to be more useful to measure the spectroscopic factor Nsub(eff) than in the region below 100 MeV since the attenuation is considerably larger (approximately 10³) in the latter case. (Auth.)