This study was conducted to investigate the effects of thermal manipulation at 5days of age and short-term fasting during the warmest part of the day on responses to prolonged heat stress of broilers. A total of 240-day-old Ross 308 female broiler chicks were divided into three groups: control, thermal manipulation (chicks were exposed to 36 degrees C for 24h at 5days of age) and short-term fasting during the warmest part of the day (10.00-17.00h). Prolonged heat stress was induced daily from 28 to 42days by heating until the ambient temperature reached 32-35 degrees C between 10.00 and 17.00h. Both thermal manipulation and short-term fasting resulted in a decrease in rectal temperatures and haematocrit values at 35 and 41days of age. Thermal manipulation improved body weight, feed consumption and feed conversion. However, short-term fasting caused a reduction in body weight and a deterioration in feed conversion. Short-term fasting lowered the percentages of carcass, whereas thermal manipulation highered breast yield. Both thermal manipulation and short-term fasting decreased heart mass and abdominal fat.