The wheat leaf rust (Puccinia triticina Eriks.) adult plant resistance gene Lr22 was discovered in the wheat relative Aegilops tauschii Coss. and transferred to Triticum aestivum L. in the 1960s. It was subsequently found to be allelic to a resistance gene in the wheat cultivar ‘Thatcher’ and was named Lr22a, while the allele in ‘Thatcher’ was named Lr22b. Both genes are adult plant resistance genes, however Lr22a provides effective resistance against all Canadian P. triticina isolates to which it has been tested, whereas Lr22b conditions resistance only to a few rare virulence phenotypes. Lr22a has been incorporated into some Canadian and international wheat cultivars, but the presence of Lr22b has largely not been determined in Canadian wheat. Recently Lr22a has been cloned and sequenced. To genetically analyze Lr22b, ‘Thatcher’ seed was treated with a mutagen, then subsequent generations were screened for susceptibility to an Lr22b avirulent isolate, both in the field and in the greenhouse. Potential mutants were identified and will be characterized genetically. Some of these lines appear to be fully susceptible, but most have a partial level of resistance. Wheat cultivars were also screened for resistance to an Lr22b avirulent isolate to determine which lines carry Lr22b, and to discover if there are other alleles at this locus.