Serum prolactin (PRL) levels after drinking 0.75 ml/g of ethanol were observed in 44 nonalcoholic young men who had an alcoholic first-degree relative and 44 controls lacking a family history of alcoholism. The data reveal a significant increase in PRL by 30 min with a return to base line for the family history negative (FHN) men by 90 min but a further decline until 150 min for the family history positive (FHP) individuals. The interaction between family history status and time for prolactin was significant at the p = 0.008 level and the changes in this hormone after drinking was significant for both groups at the p less than 0.0001 level. These results are consistent with an effect of a moderate dose of ethanol on PRL levels and further characterize differences in reactions to ethanol for men at higher and lower risk for the future development of alcoholism.