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Heat stress experience by broilers was examined under tropical conditions using Akure, Nigeria (7° 15’N, 5° 17’E), as a case study. One hundred and eight (108) of 4-weeks old broilers (Ross 308) were used for the study. The broilers were stocked at 6 broilers per cage in 18 cages in an open sided naturally ventilated poultry house and commercial feed (crude protein: 210g/kg; ME: 13 MJ/kg) and water were provided ad-libitum. The trial was conducted between 3rd and 22nd February 2003. February was chosen because it is usually the hottest month in the year in Akure. The air temperature, relative humidity and wind speed were measured inside and outside the poultry house for the period. A temperature humidity index (THI) chart for broiler was used to categorize the thermal heat stress regimes experienced by the broilers. Out of the five categories of thermal regimes on this chart only three (comfort, moderate heat stress and high heat stress) were characterized.  The birds in the cages at the lowest level were comfortable for about 4 % of the study period while those in the middle and topmost cages were comfortable for about 12 and 34 %, respectively. Also the birds in the cages at the lowest level were only moderately stressed for about 64 % of the study period while those in the middle and topmost cages were moderately stressed for about 60 and 43 %, respectively. Birds in the cages at the lowest level were highly stressed for about 32 % of the study period while those in the middle and topmost cages were highly stressed for about 28 and 23 %, respectively. Panting and core body temperature were also observed to increase with increasing ambient temperature above 28 °C. These results showed the tropical conditions that are prevalent in Akure were not clement to the birds for optimum comfort and performance. However, in the meantime, these data sets will be useful in growth models as well as the design of low cost environmental management systems for improved broiler productivity in Nigeria.