Abstract: Selection for faster growth rate is accompanied by changes in the humoral and cell-mediated immunity that may potentially affect the overall immune response. The goal of the present study was to compare the carcass characteristics and immune response of four modern broiler strains. Four different genetic lines of meat-type chicks (125 Avian, 125 Arbor Acres, 125 Cobb and 125 Hubbard) were reared under similar managerial, environmental and hygienic conditions during summer season of Egypt. The high and low ambient temperatures recorded during experimental period were 32.7 and 27.8oC, respectively. The present results revealed that the Cobb and Avian broiler chicks had significantly heaviest marketing body weight compared to remaining strains. The Arbor Acres strain recorded significantly lowest breast muscle percentage compared to other strains. With respect to Cutaneous Basophilic Hypersensitivity (CBH) response, it could be observed that the Cobb strain had a greater dermal swelling response to Phytohemagglutinin-P (PHA-P) followed by Hubbard one when compared to other strains at 24 and 48 h post injection. The Hubbard strain exhibited greater bursa and spleen (as a percentage of live body weight) compared to the Avian ones. The mortality rate of Arbor Acres strain was the highest than those of other broiler strains. We concluded that some parameters of immunocompetence could be considered as a selection criterion when selecting for productive performance under high ambient temperatures.