Attention has been focused on the possibility of an interaction between the endorphinergic system and ethanol intake. In the present study, the effects of subcutaneous (SC) administration of beta-endorphin (beta-E) (0.25, 1 and 5 micrograms/kg) and/or naloxone (NX) (1 or 2.5 mg/kg) on ethanol preference (EP) have been investigated in rats. Under our procedural conditions, rats developed ethanol preference (EP) by a forced ethanol drinking session (conditioning session). Preconditioning administration of beta-E (1 microgram/kg) reduced later EP. When beta-E was administered postconditioning, the opioid affects ethanol preference depending on the dose: both 0.25 micrograms/kg and 5 microgram/kg reduced EP, but the dose of 1 microgram/kg did not alter it. Administration of beta-E (1 and 5 micrograms/kg) before the first testing session attenuated EP. NX antagonized the effects of beta-E on EP in the three experimental procedures used, indicating that mu-opioid receptors might be involved in the beta-E-induced reductions on EP. Our results provide further evidences for a beta-endorphinergic system involvement on the mechanism leading to consumption of ethanol.