We are investigating a new method to determine the polarization of proton beams accelerated to high energies by measurements after deceleration to low energies, where simple and precise techniques can be used based on the large and well known analyzing power of pp elastic scattering. The polarized proton beam of SATURNE II was accelerated to 520 MeV and its polarization was measured by extracting the beam onto the NN beam line polarimeter.The beam was then accelerated to 800 MeV, decelerated to 520 MeV and again extracted. The loss in polarization is due to crossing twice the intrinsic depolarizing resonance γG = 3 at 631 MeV with adiabatic spin flip, once during acceleration and once during deceleration. The depolarization was intentionally increased by partially correcting the resonance, thus making the adiabatic flip less complete. The correction was introduced either at the rise or at the descent. The final polarization was the same in both cases showing that the depolarization was, as expected, the same during acceleration and deceleration. Another measurement was performed between 880 and 1200 MeV crossing successively two intrinsic resonances γG = ν zat ⋍900 Mev and γG = 4 at 1145 MeV. Here the polarization at 1200 MeV was measured directly and is compared to the value calculated from the measurements at 880 MeV before accelerating to 1200 MeV and after decelerating from 1200 MeV, assuming symmetric depolarization. The measured and the calculated values agree with ∆PB = 0.03 at P B ⋍ 0.75 .