This experiment had the goal to analyze responses to various sources of stress (weaning, exposure to heat and pre-slaughter mixing) in the third generation of selection of two lines of pigs genetically selected on the basis of plasma cortisol levels (“high” or “low”) measured one hour after injection of adrenocorticotropin. This test assesses the activity of the adrenocortical axis, a major endocrine system of the stress response. Results show that the high line had a significantly lower post-weaning growth rate. However, its growth rate was higher in the late fattening period, so that the two lines had the same overall growth rate throughout their productive lives. Prolonged exposure to heat (29.9°C vs 26.1°C) during the late fattening period (D133-D158) reduced the growth rate of animals to the same extent in both lines. Group-mixing stress prior to slaughter increased cortisol levels measured in urine collected from the bladder as well as skin lesions on carcasses, and increased muscle pH measured 24h after slaughter. These consequences of pre-slaughter mixing, however, did not differ between lines. These results show that responses to different sources of stress are affected in different ways by the level of adrenocortical activity. Associated with production data, they will allow evaluation of the relevance of this selection criterion for increasing animal robustness.