Stereotypies such as bar-biting and sham-chewing, inactivity and unresponsiveness are behavioural responses to confinement in pigs. A link between stereotypies and opioids in sows, has been established by Cronin et al.,(1986) who found that the opioid antagonist naloxone inhibited some stereotypies. Stereotypies exhibited different degrees of resistance to the disruption by naloxone, in Cronin's experiment. Modulation of opioid receptors can be influenced by chronic treatment with opioid agonists and antagonists (Blanchard, and Chang,1988). Similarly, opioid receptors can be up or down-regulated by stressful stimuli such as restraint, electric footshock or social isolation (Zeman et al., 1988). In the study reported here mu, delta and kappa receptor densities and affinity were measured post-mortem. A comparison was made between sows which had been tethered or group-housed on commercial farms. The receptor densities were also compared with the behaviour which tethered sows had shown during the latter stages of pregnancy, as well as with their reproductive peformance.