Noise has been shown to be a potential source of stress for pigs. The aim of this study was to determine the effect that chronic exposure to noise would have on pigs’ stress hormone levels and behaviour. Twenty-four barrows were divided into three treatments: N1 was exposed to 2h of broad-band noise (90dB) daily, N2 was exposed to the same source of noise but only three times a week, and the third treatment were handled in a similar manner but were never exposed to the noise. Blood samples were taken weekly before, during and after exposure to the noise. The blood samples were analyzed for adrenaline, noradrenaline, ACTH and cortisol concentrations. The behaviour of the pigs was documented using video recordings. The first exposure to the noise caused a change in the pigs’ behaviour, the showed increased movement and lied down less, but this did not coincide with a change in the pigs’ stress hormone concentrations. After four days of exposure to the noise, the pigs in the N1 treatment showed an increase in plasma ACTH and cortisol levels, while the same hormone concentrations did not increase until day 11 (third exposure) in the N2 treatment. The pigs in the N1 had an increase in the noradrenaline/adrenaline ratio of the eleventh day of exposure. Once again, the N2 treatment experienced a delay and the ratio did not increase until day 18 or the fourth exposure. In both treatments exposed to the noise, the amount of social behaviour (ie. nosing other pigs) decreased and the amount of time they spent lying increased. Both of these treatments also experienced a decrease in daily gain. Further examination using sixteen barrows found that chronic exposure to noise resulted in a time dependent shift in the adrenocortical and sympathetic neural systems response. When challenged cortisol concentrations rose and fell at a faster rate. When the pigs were restrained the adrenaline, noradrenaline and ACTH concentrations increased and decreased at a faster rate while elevation of cortisol concentrations was delayed. The authors concluded that repeated exposure of pigs to noise levels should be avoided, as it can be a potential source of stress for pigs.