1. A total of 100 patients were treated for anxiety or neurotic depression with carbon dioxide combined with psychotherapy or with psychotherapy alone.2. Of 50 patients treated with carbon dioxide, two-thirds showed no change, one-third improved, none could be classified as having recovered socially.3. Of 50 control patients treated with psychotherapy alone, three-fourths showed improvement or social recovery and one-fourth showed no change.4. Patients treated by psychotherapy alone showed improvement on fewer treatments.5. The explosive abreaction following administration of carbon dioxide could not be integrated into the patients' defense mechanisms.6. The use of carbon dioxide therapy in our hands added no specific therapeutic effect but did add problems of transference and resistance that retarded or prevented recovery.7. Treatment of patients with symptoms of anxiety or neurotic depression was best accomplished by psychotherapy alone.Abstract Teaser