[en] In most cases requirements on the accuracy of the important fast fission cross sections for fast reactors have not yet been attained. The adequacy of fast fission cross section evaluations are most conveniently tested by computing integral measurements in benchmark fast critical assemblies. Results of sensitivity analyses of the U and Pu fission cross sections for two large benchmark fast critical assemblies (ZPR6-A and ZPR6-7) are presented herein. These sensitivity coefficients emphasize the importance of fast fission cross sections in fast reactor design and, along with the benchmark tests, point out the continued need for improvement in the evaluation of fast fission data