The levels of dynorphin, α-neoendorphin and β-endorphin immunoreactivity (ir-DYN, ir-α-NEO, ir-β-E) were measured in the brain, pituitary and gut of rats subjected to a variety of manipulations. Water deprivation caused an increase in the ir-DYN and ir-α-NEO content in the hypothalamus and a decrease in the neurointermediate (NI) lobe of the pituitary. The ir-β-E level decreased in the hypothalamus and anterior lobe of the pituitary, while it increased in the Nl-pituitary. Food deprivation, as well as chronic fenfluramine (10–20 mg/kg) treatment increased, while acute muscimol (0.5 µg/10 µl) treatment decreased the ir-β-E, but not ir-DYN or ir-α-NEO content in the hypothalamus. The anterior pituitary content of ir-β-E was increased after food deprivation and decreased after chronic fenfluramine treatment. However, the ir-DYN and ir-α-NEO contents in the duodenum were markedly increased after food deprivation, while chronic fenfluramine treatment led to a dramatic decrease in the ir-DYN content. These results suggest that the levels of opioid peptides in the brain, pituitary and gut may be differentially and independently affected by alteration of the inges