In situ hybridization and specific radioimmunoassays were used to study the influence of ethanol on proopiomelanocortin (POMC) and prodynorphin (PDYN) biosynthesis in the rat pituitary. Repeated intragastric ethanol administration (starting with a total daily dose of 5 g/kg every 2nd day, until a dose of 10 g/kg was attained on the 10th day and that dose was maintained by the 19th day) resulted in a reduction in the POMC mRNA level (about 20%) in the intermediate lobe of the pituitary (3 h after the last dose), whereas the level of β-endorphin in the neurointermediate lobe was attenuated (by about 32%) only during the withdrawal (48 h after the last dose). Additionally, the plasma level of β-endorphin after repeated ethanol and during withdrawal was significantly reduced (by about 44 and 66%, respectively). No changes in the POMC mRNA or the β-endorphin levels were detected in the anterior lobe. In contrast, the PDYN mRNA level was found to be decreased in the anterior lobe during the withdrawal (by about 43%). This decrease was in conjunction with an increase in the α-neoendorphin level (by about 57%) in that lobe. The PDYN mRNA level in the intermediate lobe and the α-neoendorphin level in the neurointermediate lobe were unchanged after ethanol, as well as during the withdrawal period. Acute ethanol (5 g/kg) decreased the level of β-endorphin in the anterior lobe; this effect being associated with an elevation in the peptide level in plasma. On the other hand, acute ethanol had no effect on the POMC and PDYN mRNA levels, nor did it affect the α-neoendorphin concentration in the pituitary. The results of our study indicate that acute and repeated ethanol differentially affects the biosynthesis of opioid peptides in the specific lobes of the pituitary. In the light of an opioidergic local regulation of endocrine secretion, these effects may participate in hormonal disturbances which are common in chronic alcoholics.