A number of studies point at platelet monoamine oxidase (MAO) activity being reduced in alcoholics with a family history of drinking, this being a possible vulnerability marker for alcoholism. To test this hypothesis, we examined a group of recently detoxified alcoholics with high (n = 25) and low genetic loading for alcoholism (n = 28) and a group of healthy controls (n = 21). Clinical assessments were made using the SCID II interview for psychiatric disorders, the Family History Assessment Module and the Semi-Structural Assessment of Genetics in Alcoholism, a questionnaire especially designed for genetic studies. Platelet MAO activity with and without ethanol stimulation and the percentage of MAO activity with ethanol did not differ between groups. The only significant difference was a lower inhibition of MAO activity with ethanol in alcoholics both with and without a family history compared to controls. In patients with antisocial personality traits, platelet MAO activity was also not found to be different from other alcoholics. Our findings question the hypothesis of reduced platelet MAO activity to be a possible vulnerability marker for alcoholism. Copyright (C) 2000 S. Karger AG. Basel.