The assessment of well-being is of prime importance in the development of new production systems. For meaningful conclusions to be drawn, every aspect under the broad headings of physical, physiological and behavioural well being should be studied. There are a number of instances where, in extreme circumstances, physiological parameters have been shown to affect health and production, and are considered by some to be useful in determining long term welfare status. There is, however, evidence to suggest that the interactions between physiological functions are too complex to allow simple conclusions. As part of a comprehensive study into welfare of group housed gilts (Stewart et al 1993) this paper describes the results of an immune challenge, an adrenal function test (ACTH challenge) and adrenal weight and how they are associated with other welfare parameters.