This study was carried out at the Experimental Farm of the Animal Physiology Research Lab, Faculty of Agriculture, Cairo University, during the summer season of 2004. The objective was to assess the relevant physiological responses and growth performance of Egyptian buffalo-calves to artificial constant severe heat stress. Eight buffalo-calves were randomly divided into lab A and lab B, their age and live body weight were 6 months and about 119 kg, respectively. All calves were assessed under two constant thermal conditions, heat stress (40 °C and 87.5% RH, lab A) and comfort state (25 °C and 64.5% RH, lab B). Two trials were conducted, each one continued for one month in each lab. They were interrupted by 15 days under natural climatic outdoor conditions. Values of Ht, Hb and RBCs were reduced by heat stress during the two trials. The white blood cells count (WBCs) were significantly increased (around 50%). Levels of total protein (TP), albumin (Alb), total lipids (TL), triglycerides (TG), total cholesterol (TC), glucose (Glu) and blood urea nitrogen (BUN) were decreased by heat stress during the two trials, while, the globulin (Glo) level was not affected. In the two trials, heat stress caused slight increase (4 to 8 %) in sodium (Na) and potassium (K), and increase (47 to 58 %) in phosphorus (P) level, and calcium (Ca) was decreased by 20%. In both trials, heat stress decreased insulin (Ins), increased glycogen (Glg) and both triiodothyronine (T3) and thyroxine (T4) were dropped by about 50%. It can be concluded that buffalo-calves were able to maintain their lives with some chemical and physical changes that led to the delay in growth when exposed to high temperatures.