We report measurements of the magnetic moment of YBa2Cu3O7-delta films when subjected to injection of short pulses of spin-polarized current from the colossal magnetoresistance (CMR) manganites La0.7Ca0.3MnO3 and La0.7Sr0.3MnO3, and unpolarized current from the nonmagnetic perovskite LaNiO3(LNO). We study relaxation from the Bean critical state, with and without current pulses. For pulses longer than 100 ms, the effect of injection is similar for all samples and is due to heating. Below 1 ms, we see a clear difference between the CMR and LNO samples and attribute this to the spin polarization of the current injected from the CMR materials. (C) 2001 American Institute of Physics.