1. One hundred and thirty-three patients were treated experimentally with carbon dioxide therapy. The Meduna and rapid coma techniques were used exclusively. Twenty per cent of the patients received simultaneous psychotherapy.2. Prior to carbon dioxide therapy, one-third of all the patients had received psychiatric treatment unsuccessfully.3. The clinical results of rapid coma techniques were superior to those achieved by the Meduna technique; using the Meduna technique, 22% of a neurotic group improved clinically, whereas, 50% improvement in a comparable group was achieved with rapid coma techniques. Forty-seven per cent of a group of 15 obsessive compulsive neuroses improved clinically when treated with rapid coma technique. Of a group of 24 schizophrenics, 33% improved clinically with rapid coma therapy.There appeared to be no significant influence on the over-all results whether the patient had previous or concurrent psychotherapy in relation to carbon dioxide therapy.4. Carbon dioxide therapy with the Meduna technique was ineffective in treatment of a group of 5 cerebral palsy and 2 dystonia musculorum deformans patients. One cerebral palsy patient was treated unsuccessfully with rapid coma.5. The diagnosis of treatment anxiety and its management is essential to the armamentarium of the carbon dioxide therapist.