Compared to other species of farm animals, pigs are more sensitive to high environmental temperatures, because they cannot sweat and do not pant so well. Furthermore, fast-growing lean pigs generate more heat than their congeners living in the wild. This, in combination with confined housing, makes it difficult for these pigs to regulate their heat balance. Heat stressed pigs have low performance, poor welfare, and, by pen fouling, they give higher emissions of odour and ammonia.Above certain critical temperatures (inflection point temperatures) pigs start to adapt their mechanisms of balancing heat loss and heat production. The inflection point temperatures above which the responses change may well differ depending on which animal parameter is studied. Within this thesis, firstly, these critical temperatures were determined for different physiological, behavioral and production parameters. Secondly, the effect of different cooling systems on these parameters was studied.In order of appearance we found inflection point temperatures for lying on slatted floor, respiration rate, evaporative water, ratio of water to feed intake, total heat production, activity heat production, voluntary feed intake and rectal temperature. These inflection point temperatures were different for the different parameters and show the subsequent strategies the pig follows at increasing temperatures. Relative humidity had minor effects on physiological parameters. However, a combination of high relative humidity and high temperature showed a detrimental effect on daily gain.Theavailability of cooling systems, e.g. floor cooling, water bath or sprinklers, had beneficial effects on pigs' performance.It is concluded that high ambient temperatures strongly affect physiology, behaviour and performance of growing pigs.The inflection point temperatures found in this study are good indicators of heat stress. These can be used as set points for cooling systems. Cooling systems improve animal performance and welfare under high temperature conditions.