WI٢٢٩١ and Tadmor, two barley lines widely grown in the Mediterranean region were tested for powdery mildew (Erysiphe graminis f. sp. hordei) resistance together with the European differential tester set against six powdery mildew isolates. The six cultures of powdery mildew developed from single colonies were comprised of four powdery mildew isolates originating from Syrian barley lines and two cultures originating from Danish barley lines.