Heat stress is a condition in which the body temperature is so high that it interferes with normal body functions, and leads to extreme physical exhaustion and death. Heat stress is a major cause of mortality in our country. Summer season, associated with thick layer of feathers on the body of the chickens and absence of sweat glands, make them highly prone to heat stress. Additional factors include too low height of ceiling, inadequate ventilation, overcrowding, absence of vegetation or trees or creepers to cool the air in and around the poultry farms.Birds are particularly susceptible to high temperatures, when accompanied by increased humidity. As birds lack sweat glands, their only method of cooling is rapid respirations with open mouth. If the body temperature rises, birds become exhausted, and die from respiratory, circulatory or electrolyte imbalances.Symptoms include open mouth breathing and panting. Later the birds show weakness, incoordination and ultimately die after paralytic symptoms. Mortality may reach up to 100 percent.Treatment includes dipping of birds in chilled water or chilled water may be introduced orally in to their crops by a thin polythene tube attached to a syringe. Air movements, in the form of ventilation and fans, or sprinklers and foggers, facilitate heat loss. Give vitamins in increased amounts, particularly Vitamin E and C. Give also electrolytes, as heat stress creates electrolyte imbalance. Every effort should be made to increase circulation of air by running ventilation equipment, such as fans.Prevention includes provision of insulated roof, high ceiling, planting of creepers to cover the roof, provision of enough cold water in summer, adequate ventilation, use of air coolers, exhaust fans, water sprinklers. Overcrowding of birds may also be avoided.It is very important to control heat stress. Otherwise, apart from the direct losses, such a flock may also suffer from a number of infectious diseases on account of the lowered resistance from heat. This, in turn, will further increase the losses and ruin farmer’s economy.