Quantitative receptor autoradiography was used to measure differences in [3H]DAGO binding to mu-opioid receptors in selected fore- and midbrain regions of chickens subject to varying degrees of chronic food restriction: either R (a recommended restricted ration), 2R (twice recommended restricted ration) or AL (ad libitum). A significant increase in binding of 75% was observed in the paleostriatum primitivum (a homologue of the mammalian globus pallidus) with the R treatment compared to the 2R and AL treatments. This finding concurs with results of earlier pharmacological manipulations with opioid antagonists, which indicated that activation of mu-opioid receptors plays a contributory role in reinforcement of post-feeding oral stereotypies in chickens subject to the same R treatment.