Host: parasite interaction of twenty barley cultivars and E. graminis f. sp. hordei was studied at different environmental conditions and growth stages. At seedling stage, the low reaction of cultivar Atlas 68, Akrik, Baladi, Charlot town, G. A. 3694, G. A. 9737, black Chinese, white hybrid, and v. well were reflected in the lower values of infection types. However, resistant reaction was proved only on Atlas 68, Baladi, G.A. 9737, and Black Chinese at heading stage. Meanwhile, at field conditions during three consecutive seasons, the later cultivars showed mildew resistance regardless the adult stages. These cultivars might be of great value as source of resistance in any breeding programme. Moreover, our data indicated that mildew races in Iraq could be different from those found in other regions of the world.