Résumé : The Q-region of Kππ mass (i.e. 1.10 ≤ M(Kππ) < 1.5 GeV) is studied for the reactions K+p → K+π+π-p (≈ 77 000 events) and K+p → Kseen0 π+π0p (≈ 19 000 events). The data samples correspond to K+p interactions at fourteen beam momenta in the range 2.5 - 12.7 GeV/c. The production and the decay of the of the Kππ system are analysed as a function of the incident energy and the Kππ mass. It is shown that the differential cross section dσ/dtpp shrinks when the incident energy increases. The spin-parity is found to be predominantly 1+ for the whole Q-region and the density-matrix elements do not vary with the energy or the Kππ mass. The ratio of the number of Kρ{variant} to the number of K*π events is obtained from a fit of the decay Dalitz plot and found to be maximum for 1.25 ≤ M (Kππ) < 1.30 GeV. © 1972.