If a housing condition results in impaired immune system function then vulnerability to disease is greater in that condition. Measures of immune system function can therefore be important indicators of welfare. Another indicator of welfare is the maximal adrenal cortex response to ACTH challenge. Ten third parturition sows kept in stalls, and 27 first parturition sows kept in an electronic sow feeder system have been studied. A direct measure of immune system function is to assess B-cell responses by measuring antibody production following antigen challenge. Sows in stalls were injected with tetanus toxoid, as commonly practised for protection against tetanus. The amount of antibody produced was negatively correlated with adrenal weight. The colostral antibody ELISA titre was 1/125,000 when the response to ACTH challenge was zero but was almost zero in animals which showed an increase in salivary Cortisol of 25 nmol l-1 after ACTH challenge i.e. antibody production was negatively correlated with adrenal response (r = -0.634, p = 0.028 (Fig. 1)).