A survey of variability in reaction to 2 rust pathogens was conducted on 121 accessions of cultivated and wild forms of T. monococcum. On the basis of disease reactions certain accessions were chosen for inheritance studies. All the accessions were highly resistant, or resistant, to P. recondita. Susceptible transgressive segregates could not be identified when hybrid populations from crosses between accessions with slightly differing reactions were examined. As F1 hybrids between diploid wheat and tetraploid or hexaploid wheats, as well as an AAAABB amphiploid, produced high reactions, it is apparent that transference of resistance to P. recondita from diploid wheat to wheats of higher ploidy will be difficult. The results of tests on the T. monococcum collection with P. graminis tritici cultures and genetic studies on 35 of the accessions producing low reactions with at least some cultures showed that 2 genes for resistance, Sr21 and Sr22, could be easily recognized. One exceptional accession, C69.69, produced an atypical reaction pattern and presumably possesses a gene(s) other than Sr22. The low reaction of the standard differential stock W10 is attributed to a single gene, Sr21. On genetic analysis some accessions with reaction patterns similar to W10 gave skewed segregation ratios or ratios indicative of duplicate or triplicate genes. However, no gene other than Sr21 was isolated or identified among the monogenic accessions studied. Therefore an alternative explanation that deviation was due to abnormal gametic segregation or transmission was preferred.