There is a considerable inconsistency in terms of the association between alcoholism and alterations in monoamine oxidase (MAO) activity. The main objectives of this study were to investigate the changes in platelet MAO-B activity throughout the alcohol withdrawal period and whether or not MAO-B activity differed between patients with high- and low-aggression tendency. We assayed platelet MAO-B levels spectrophotometrically in 22 male inpatients with alcohol dependence in their first and fourth weeks of withdrawal and in 20 healthy controls. Patients were divided into two high- and low-aggression subgroups according to scores obtained in a Brown-Goodwin Assessment for Life History of Aggression. Our data revealed that the significantly lower platelet MAO-B activity observed during the first week of alcohol withdrawal in patients, compared to controls, did not continue in the fourth week, and that there was no relationship between aggressiveness and MAO activity. These results suggest that low platelet MAO activity may be a state marker of alcohol withdrawal period or a result of high alcohol consumption rather than a trait marker of alcoholism.