The levels of immunoreactive, β-endorphin (ir-β-EP) were measured in the brain and pituitary of lean Zucker rats subjected to food deprivation for 72h and to a high fat diet, and in fatty Zucker rats after food deprivation for 72h. ir-β-EP was increased in the neurointermediate (NI-) pituitary lobe but reduced in the edulla-peons of fatty rats when compared to lean littermates fed ad libitum. Food deprivation decreased ir-β-EP in the cortex and medullapons of lean rats and in the cortex, midbrain and NI-pituitary of fatty rats. In contrast, ir-β-EP was increased in the anterior pituitary of lean rats and in the striatum of fatty rats after deprivation. The high fat diet produced a decrease in ir-β-EP in the cortex, midbrain and NI-pituitary with an increase in the striatum and hypothalamus of lean rats. These results suggest that the ir-β-EP concentration could be diffrentially affcted in different brain regions of Zucker rats by changes in the energy balance.