1. Twelve Large White x Landrace male pigs, six with high adrenocortical response to ACTH, and six with low response, were subjected to mild and moderate exercise, and then to insulin-induced hypoglycaemia. 2. Plasma ACTH, cortisol, catecholamines and some haematological and plasma biochemical parameters were determined in response to exercise, and glucose and cortisol in response to insulin challenge. 3. High responders had significantly greater increases than low responders in ACTH, cortisol and catecholamines following exercise, and in cortisol following insulin challenge. 4. The results suggest that differences in adrenocortical response to exogenous ACTH are an accurate reflection of the animal's response to stressful stimuli.