This experiment was conducted to study the possible beneficial effects of diazepam, a mild tranquilizer and appetite stimulator drug, on food intake and the physiological homeostasis of broiler chicks exposed to high ambient temperatures of the summer months.                 A total of 200, one day old, unsexed Hubbard broiler chicks were used. The chicks were allocated into five equal groups, one of them was kept as control while the others received different gradient levels of diazepam for 6 weeks.                 The results indicated that both live body weight and body weight gain at the end of the experiment (6 wk) were significantly higher for birds at 0.5 gm/L of drinking water than the control and the other treatment groups. Changes in live body weight from 0 to 6 weeks of ages were 34.3; 37.7; 43.6; 40.2 and 37.9 folds for the control; 0.25; 0.50; 0.75 and 1.0 g/L doses, respectively.                 A significant increase in feed consumption was observed for birds treated by 0.50 gm/L of the drug at different ages. Similar trends were also observed for feed conversion ratio, protein consumption and efficiency of protein utilization in treated groups.                 A significant dose dependent increase in _T4 and _T3 levels at 4 and 6 weeks of age was also observed. Plasma total protein; triglycerides; cholesterol; creatinine; GOT and GPT levels were significantly different among treatment groups, except for the lower dose, and the control one.                 Rectal temperature was significantly higher in the control and the 0.25 gm/L of diazepam groups than the other groups. Treated birds were also more resistant to the deleterious effects of high ambient temperature, as indicated by their significantly, dose-dependent, lower H/L ratios in blood. Moreover, mortality rate was higher (10%) in the control group than in all treatment groups, where no mortalities occurred.                 It could be concluded that, under hot summer conditions, water supplementation of 0.50 gm/L of  diazepam is desirable to stimulate eating behaviour of broiler chicks, and to maintain their physiological equilibrium during high  ambient temperatures.