AbstractMajor genes for resistance to powdery mildew were analysed in 24 Czechoslovakian wheat cultivars and, in part, in their parents. For this purpose individual isolates of the pathogen, able to differentiate host lines with known resistance genes, were selected. Eight of nineteen winter wheat cultivars do not possess any major resistance gene. Three cultivars have one and seven have two genes. One cultivar carries a combination of three genes (Pm2, Pm4b, Pm8). The most common resistance genes arePm4b, Pm5 and Pm8. Pm2is once combined withPm6. Only one of five spring cultivars lacked a major resistance gene.Mlkis once present alone and twice combined withPm5. There is one spring cultivar with a novel combination of three genes:Pm1, Pm5and another gene needing further characterization. The observations are discussed with additional results of parent lines and further information on pedigrees.