The winter wheat (Triticum aestivum L.) line CI13227 with slow rusting resistance to leaf rust, caused by Puccinia triticina Eriks., was crossed and backcrossed to 'Thatcher' (Tc) wheat. Backcross F 2 families were tested for seedling resistance and segregated in a 1:1 ratio for families that segregated for resistance and families that were homozygous susceptible. The BC 1F 2 resistant seedlings were progeny tested for infection type (IT) as BC 1F 3 lines and compared for IT with near-isogenic lines of Tc with alleles at the Lr3 locus. The BC 1F 3 lines and the Tc line with Lr3ka had nearly identical IT. The F 2 progeny of a resistant BC1F3 plant and a Tc line with Lr3ka did not segregate for IT confirming that CI13227 had an allele at the Lr3 locus. The BC 1F 2 plants from families that were homozygous susceptible as seedlings were tested as adults for leaf rust IT. Resistant BC 1F 2 adult plants were selected and advanced to BC1F6 by single seed descent. A single BC1F6 plant was crossed with Tc, and the Tc*3/CI13227 population advanced to F 6. The F 6 recombinant inbred lines (RILs) were tested for leaf rust resistance at two locations. Molecular mapping with Diversity Arrays Technology (DArT) and simple sequence repeat (SSR) markers detected a major locus for resistance on chromosome 1BL. A polymerase chain reaction (PCR) marker specific for Lr46 also mapped in the 1BL region associated with resistance. Quantitative trait loci on 2DS, 2B, and 7BL for slow rusting resistance in CI13227 detected in previous experiments were not detected in this study. CI13227 has seedling resistance gene Lr3ka and likely has the adult plant resistance gene Lr46.