The present study was carried out at the Department of AnimalWealth Development, faculty of Veterinary Medicine, Zagazig University The aim was to study the genetic resistance to Newcastle disease and Fowlcholera among purebred Lohman Selected Leghom (LSL) and, Fayoumi(FF). This study revealed the following main points: Fayoumi cockerels had significantly higher fertility percentage compared with those of Lohman Selected Leghom (LSL) (88.70 vs.81.33 %). Non-significant differences for hatchability percentage were found among purebred, crossbred and reciprocal crossbreds. In additionnegative heterosis was estimated for crossbred and reciprocalcrossbreds (-0.57 % and -7.88 %) on average. Body weight of purebred LSL had significantly the lowest estimatesamong purebreds and crossbreds at two, four, eight and 12 weeks ofage (123.2, 183.2, 423.2, and 613.2 gm; respectively). The highestsignificant values were recorded for FL crossbred (152.73, 277.73,647.73 and 897.73 gm; respectively).Positive heterosis estimates were recorded for FL crossbreds andreciprocal crossbred LF across the ages (12.46 and 9.86 % , 25.78and 17.39 %, 32.65 and 3.25 %, 28.10 and 4.05 %) at two, four,eight and 12 weeks of age; respectively