Various polymorphisms of the X-chromosomal monoamine oxidase A (MAO-A) gene were investigated for association with affective disorders. However, none of the studied variants could consistently be associated with either major depressive or bipolar affective disorder. Recently, a positive association between panic disorder and a novel functional repeat polymorphism in the MAO-A gene promoter, with the longer alleles being more active, was reported. Since monoaminergic neurotransmission is supposed to play an important role in affective disorders, we investigated a potential association of this polymorphism with major depressive illness in a sample of 146 unrelated patients of German descent and a control group of 101 individuals with a negative life history for affective disorders. Similarly to the recent findings in panic disorder, we observed a significantly increased frequency of genotypes containing only long alleles in female patients with recurrent major depression in comparison with age- and sex-matched controls. Thus, our data suggest that an excess of high-activity MAO-A gene promoter alleles resulting in an elevated MAO-A activity is a risk factor for major depressive disorder in females. Am. J. Med. Genet. (Neuropsychiatr. Genet.) 96:801-803, 2000.