This study was undertaken in the variety Yaqui-53 to find the chromosomes carrying genes for resistance to three races of black rust. Critical monosomic analysis indicated (a) that resistance to race 15 is governed by a single factor located in chromosome 3B and a minor gene conferring additional resistance is present in chromosome 6D (b) Yaqui-53 carries two dominant genes for resistance to race 34 in chromosome 2A and 7B (c) Resistance to race 122 is conditioned by three genes located in chromosome 3A, 3B and 6D.