The Newcastle Anxiety Depression Diagnostic Index (NADDI) was applied to 151 patients who received a monoamine oxidase inhibitor (MAOI) or a tricyclic antidepressant (TCA) drug. The pretreatment presence of a physical stressor and absence of agoraphobia were associated with superior MAOI effects. In women nine of the 13 NADDI items were associated with superior response to the MAOI drugs: these items comprised the absence of childhood anxiety, agoraphobia, compulsive symptoms, early awaking, and retardation, and the presence of dependent traits, neuroticism, physical stress, and panic attacks. In men the absence of suicidal tendencies and retardation, and the presence of dependent traits and panic attacks were associated with superior TCA effects. A within-treatment analysis indicated that depressed men responded better to MAOI than did anxious men.