Erythrocyte catechol-O-methyltransferase (COMT) activity was measured in normal and depressed populations before specific medication. In the groups of patients, anxiety and depression scores were evaluated by the AMDP rating scale. The authors found lower enzyme activity in patients with major depression, recurrent and bipolar disorder, depressed, but no change was found in dysthymic disorder when compared to control values. However, there was no relationship between COMT activity and age, anxiety and depression scores of patients. Furthermore, the subdivision into two subpopulations, one with normal COMT activity and another with lower COMT activity, did not make it possible to assign a role to the enzyme in the severity of depression. The enzyme could, however, be considered as a genetic marker of depressive vulnerability.