Low platelet monoamine oxidase B (MAO-B) activity and the presence of the Taq1 A1 allele of the dopamine D2 receptor (DRD2) gene have independently been proposed as 'biological/genetic' markers for alcoholism. In the present study, the relationship between these two markers was investigated in a group of socially stable Caucasian middle-aged men with a mean (+/-SD) daily ethanol consumption of 85 +/- 57 g. The platelet MAO-B activity was significantly lower in individuals with the DRD2 A1 allele (n = 8), compared to those without it (n = 29). This relationship remained unchanged when including only subjects who fulfilled DSM-IV criteria for alcohol dependence (n = 27). The finding suggests that alcoholics who are carriers of the DRD2 A1 allele may have lower platelet MAO-B activity.