Résumé : In this paper a comparison of the general features of the reactions K±p→Q±p (1) at incident momentum 8.25 GeV/c is presented. The relevant data derive from events yielding four-constraint fits to the reactions K±p→K±π+π-p in exposures of the CERN 2m HBC to RF-separated K+ and K- beams. The (Kππ) effective mass distributions, production angular distributions in the Q region (1.2≤M(Kππ)≤1.5 GeV) and corresponding decay angular distributions are exhibited, and background effects due to N* and Δ production are systematically studied. In particular, it is found that the distributions dσ/dt′ and dσ/dt for reactions (1) are adequately described by exponential functions over the interval 0.05-0.35 GeV2, and exhibit a cross-over effect for momentum transfer squared -0.1 GeV2. For both reactions a flattening of dσ/dt′ for t′ < 0.05 GeV2 is observed. By studying the Chew-Low plots and the effects of the different cuts it was found that this flattening cannot be attributed to amplitudes with net s-channel helicity flip different from zero, at least at these energies. © 1976.