[en] The authors review recent measurements of the high-frequency dynamic magnetic susceptibility in the high-T_c superconducting systems La_2-xSr_xCuO₄ and YBa₂Cu₃O_6+x. Experiments were performed using the chopper spectrometers HET and MARI at the ISIS spallation source. The authors have placed their measurements on an absolute intensity scale, this allows systematic trends to be seen and comparisons with theory to be made. They find that the insulating S = 1/2 antiferromagnetic parent compounds show a dramatic renormalization in the spin wave intensity. The effect of doping on the response is to cause broadenings in wave vector and large redistributions of spectral weight in frequency