Sixty-six wheat cultivars grown in Belarus, Poland, Russia and the Ukraine were tested for mildew response to a collection of 11 different isolates of Erysiphe graminis DC f. sp. tritici Marchal. Nineteen cultivars have shown a susceptible reaction and eighteen were characterized by susceptible or intermediate responses. Fourteen cultivars revealed isolate-specific response patterns that could be attributed to major known resistance genes or gene combinations. Twelve cultivars have one documented gene: Pm5 in eight cultivars, Pm2 in two cultivars and Pm8 also in two cultivars. One cultivar has two genes (Pm2 + Pm6), while another cultivar carries a combination of three genes (Pm1 + Pm2 + Pm6). Fifteen cultivars were characterized by response patterns not documented so far or by a known resistance response combined with an undocumented resistance. Apparently three cultivars with the T1BL.1RS wheat-rye translocation have a gene suppressing the Pm8 mildew resistance. One cultivar was resistant to all the used isolates. Its resistance might be conditioned by an unknown major gene or combination of genes.