Non-responders to cyclic antidepressants were treated with the MAO-inhibitor tranylcypromine in two studies: the first study in an open comparison with L-5-hydroxytryptophan (L-5HTP), the second study in a double blind comparison with nomifensine. 2. While both L-5HTP and nomifensine appeared to be ineffective, tranylcypromine was effective in 26 out of 45 patients. 3. It is concluded that besides ECT also MAO-inhibitors such as tranylcypromine are an effective alternative for depressed patients not responding to cyclic antidepressants.