Barley breeding lines and cultivars have been evaluated for their levels of sensitivity to aphid infestation under laboratory and natural in­festation conditions in the field. In 1992/93 barley season, laboratory screening of 80 barley genotypes revealed 9 resistant and 8 moderately resistant entries to the corn leaf aphid Rhopalosiphum maidis. The criter­ion for resistance was based on the average daily reproduction rate of the female aphids_ Field screening of 80 genotypes in two localities re­vealed the existence of 5 entries in Mallawi and 15 in Giza that har­boured the lowest aphid population (0-25 aphids per plant) on the least percentage of infested plants per plot. In 1993/94 growing season, la­boratory screening revealed 2 resistant and four moderately resistant genotypes to R. Maidis out of 60 entries. Field screening of the same 60 genotypes grown at Giza Resea­rch Station revealed 4 entries that were resistant to aphid build-up. Field screening of 80 barley genotypes (92/93 group) grown at Mallawi Re­search Station for the second season revealed 8 resistant entries. Five of these were found resistant in the previous season either at Giza or at Mallawi.