Cultures 70-1 and 73-47 of Puccinia recondita were selfed, crossed, and the resulting F, culture (X43) was selfed to study the inheritance of virulence on several near-isogenic lines of Triticum aestivum. Segregation of the parents, the phenotype of the F, and ratios of F2 progeny were used to explain the inheritance of pathogenicity. The F2 cultures segregated as if single dominant genes conditioned avirulence on near-isogenic lines Lr3, Lr9, LrlO, Lrl 1, Lr24, Lr27, and Lr31. The avirulence genes were usually independently inherited. linkage was only detected between virulence loci p3 and pi I, p3 and p24. and plO and p27. Two genes appeared to control virulence on near-isogenic lines with Lrl6, Lr26, and LrB. Segregation for virulence on lines with Lr29 and Lr30 fit a ratio for two complementary genes. Modifiers or inhibitors may explain this unusual ratio, A single recessive gene appeared to condition avirulence on LrlH, L.r23, and LrExchange. The F2 ratios could usually be explained by classical gene-for-gene interactions and were compatible with results obtained by selling the parents.