The present experiment was designed to study progressive changes in the physiological responses of broiler chickens (Gallus gallus) exposed to different durations of acute heat stress. Male broiler chickens (n=8) at 16 days of age, were exposed to acute heat stress of 34°C for 6, 12 or 18h while control chickens were kept at 25°C. Exposure to different durations of heat stress resulted in significant decreases in the levels of blood HCO₃^- and pCO₂, while pH and pO₂ were not changed. Hemoglobin, hematocrit and Na⁺ values were reduced after 6h while no such change was observed after 12 or 18h of heat stress. In contrast, K⁺ levels were lowered by 6 or 12h of heat stress and no differences in blood calcium levels were observed between the control and heat-stressed groups. In conclusion, there is evidence that exposure of broiler chickens to different durations of acute heat stress resulted in distinct time-dependent physiological responses. Data set from this experimental model could provide an overview of physiological state in the typical acute heat-stressed birds.