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Production performance of straight-run Cobb 500 broilers under commercial management practices were investigated. The temperature humidity indices (THIs) of these broilers at different growth stages have been developed. About 1700 birds/house were raised in three noninsulated naturally ventilated houses per trial over a 6-week growth period. Two trials were undertaken - one in winter and the other in summer. The environmental parameters measured were indoor and outdoor air temperatures and relative humidity (RH). The production responses of the birds measured were specific feed intake (FI), average body mass (BM) and mortality. The derived production responses were BM gain and feed conversion (FC). Weekly mean specific FI decreased with increasing bird age and ranged from 490 to 66 g feed/kg BM at 1 to 6 weeks of age, respectively. Weekly mean FC ranged from 5.42 to 1.24 kg feed/kg BM gain. The live weight of the birds at six weeks of age ranged from 2.30 to 1.77 kg and mortality ranged from 3.8 to 9.3%. THIs were developed for birds at 3 to 4 and 5 to 6 weeks of age and were THI3-4wk = 0.62Tdb + 0.38Twb and THI5-6wk = 0.71Tdb + 0.29Twb. These equations indicate that broilers reared under non-controlled semi arid environment were affected more by temperature than by RH.