The authors evaluated changes in serum prolactin levels as a measure of differences in response to ethanol between 30 healthy, drinking, young adult sons of alcoholics and 30 matched control subjects with no family history of psychiatric or substance abuse problems. The control subjects were matched for demographic variables, drug use histories, and alcohol use histories. Each individual was tested on three occasions, receiving, in random order, placebo, 0.75 ml/kg of ethanol, and 1.1 ml/kg of ethanol. Controlling for baseline prolactin measures and hormonal changes after placebo, the authors found that the sons of alcoholics had significantly lower prolactin levels in response to the high-dose ethanol challenge.