High level of polyamine oxidase activity is detected in sera of depressed as well as in schizophrenic patients. ECT treatment of depressed and schizophrenic patients reduced significantly the level of polyamine oxidase activity in their serAfter ECT treatment, clinically improved depressed and schizophrenic subjects were found to have sera polyamine oxidase activity not significantly differ from that of normal subjects. Possible biochemical mechanisms, which link polyamine oxidase