The effect of temperature level (248C, 288C, 328C or 368C) on performance and thermoregulatory response in growing pigs during acclimation to high ambient temperature was studied on a total of 96 Large White barrows. Pigs were exposed to 248C for 10 days (days 210 to 21, P0) and thereafter to a constant temperature of 248C, 288C, 328C or 368C for 20 days. Pigs were housed in individual metal slatted pens, allowing a separate collection of faeces and urine and given ad libitum access to feed. Rectal (RT) and cutaneous (CT) temperatures and respiration rate (RR) were measured three times daily (0700, 1200 and 1800 h) every 2 to 3 days during the experiment. From day 1 to 20, the effect of temperature on average daily feed intake (ADFI) and BW gain (average daily gain, ADG) was curvilinear. The decrease of ADFI averaged 90 g/day per 8C between 248C and 328C and 128 g/day per 8C between 328C and 368C. The corresponding values for ADG were 50 and 72 g/day per 8C, respectively. The 20 days exposure to the experimental temperature was divided in two sub-periods (P1 and P2, from day 1 to 10 and from day 11 to 20, respectively). ADFI was not affected by duration of high-temperature exposure (i.e. P2 v. P1). The ADG was not influenced by the duration of exposure at 248C and 288C groups. However, ADG was higher at P2 than at P1 and this effect was temperature dependent (1130 and 1458 g/day at 328C and 368C, respectively). In P2 at 368C, dry matter digestibility significantly increased (12.1%, P , 0.01); however, there was no effect of either duration or temperature on the digestibility of dry matter at group 248C and 328C. RT, CT and RR were measured three times daily (0700, 1200 and 1800 h) every 2 to 3 days during the experiment. Between 288C and 368C, RT and CT were lower during P2 than during P1 (20.208C and 20.238C; P , 0.05), whereas RR response was not affected by the duration of exposure whatever the temperature level. In conclusion, this study suggests that the effect of elevated temperatures on performance and thermoregulatory responses is dependent on the magnitude and the duration of heat stress.