Plasma beta-endorphin, met-enkephalin and ACTH concentrations were measured in 20 male alcoholics (age: 32-60 yr; duration of ethanol addiction: 13.2 +/- 6.2 yr; mean +/- SE) immediately after admission to the hospital (at a time not exceeding 8 hr from the last ethanol consumption) and after 5 weeks of forced abstinence. The results were compared with those obtained in 12 age-matched normal controls. Plasma ACTH and met-enkephalin levels were normal in alcoholics on both occasions. In contrast, in samples taken at admission to the hospital, the circulating concentrations of beta-endorphin in alcoholics were half (17.1 +/- 5.3 pg/ml; mean +/- SE) of those observed in the normal controls (34.1 +/- 6.0). beta-endorphin levels rose significantly after 5 weeks of abstinence (30.1 +/- 4.9); at this time, they were not significantly different from those observed in normal controls. These data indicate that acute alcohol consumption induces significant alterations in plasma beta-endorphin, but not met-enkephalin levels, which are reversed after 5 weeks of abstinence.