Ten winter wheat (Triticum aestivum L.) lines selected from the 1982 International Winter Wheat Mildew and Rust Nurseries were studied to characterize gene number and mode of inheritance of powdery mildew resistance. Two experiments were conducted: 1) each of the lines was crossed to the susceptible cultivar Chancellor, which lacks any known’ gene _ for resistance, and seedlings of the parental lines, F₁, F₂, BC₁ (Chancellor X F₁), and F₃ populations were inoculated with isolate 127 of Blumeria graminis (DC.) E. 0. Speer f. sp. tritici Em. Marchal in the greenhouse and evaluated for powdery mildew reaction; 2) the ten lines were crossed with each other and to each of 13 host differential lines with known genes for powdery mildew resistance, and 300 to 800 F₂ seedlings from each cross were evaluated. All parents were resistant (Infection Type = 1-3), except for ST1-25, which had an intermediate (IT = 4-5) reaction type. Genetic analyses of crosses revealed that the resistance in C39 and SI5 is conferred by three dominant genes (Pm2, 4b, and 6), and resistance in A55-2, R107, and Bulk PV63-6 is governed by one partially dominant gene (Pm4b). Results from F₂, F₃, and BC₁ populations derived from crosses between ‘Armada’ and Chancellor, were inconsistent, but indicated that Armada has at least one dominant gene for resistance, which likely is Pm4b as suggested by others. The resistance gene in OK75R3645 most likely is an allele at the Pm3 locus, and it is probable that the resistance gene in GO4779 is Pm1. Single recessive genes were identified in VPM1 (Pm4b) and ST1-25 (Pm8).