The effect of chronic ethanol exposure on proopiomelanocortin (POMC) mRNA accumulation, β-endorphin (β-EP) levels as well as incorporation of [3H]-phenylalanine into β-EP-related peptides was investigated in the rat hypothalamus. Animals were treated with an ethanol-containing liquid diet for 15 days. Both sucrose pair-fed and ad libitum-fed control groups were included. The levels of immunoreactive β-EP, as well as the relative proportions of nonacetyl and acetyl forms of β-EP in the hypothalami of the ethanol-treated rats were not significantly different from those in the sucrose and lab chow fed control rats. Northern blot analysis of total hypothalamic RNA indicated that ethanol-treated rats had higher POMC mRNA levels than sucrose pair-fed and control rats. Quantitation of the in vitro incorporation of [3H]-phenylalanine into POMC, β-lipotropin and β-EP by the hypothalamus, using immunoprecipitation and polyacrylamide disc-gel electrophoresis with sodium dodecyl sulfate, revealed that the increased hypothalamic POMC mRNA content was associated with increased incorporation of [3H]-phenyl-alanine into POMC by the hypothalami of the ethanol-treated rats. It is concluded that chronic ethanol can alter the expression of the POMC gene in the hypothalamus.