In contrast with the accepted definition and efficacy of coma insulin therapy, the status of subcoma therapy is still not clear. From 1942 to 1952, subcoma insulin therapy at the Payne Whitney Psychiatric Clinic was considered to be that which produced a hypoglycemia sufficient to cause clouded consciousness lasting 45-60 minutes, but stopping short of coma. It has been used in the treatment of 212 patients during this period. There was improvement in 79.7% of 133 schizophrenic patients, and in 76.9% of 26 patients with affective illnesses. It appears that, in the treatment of certain psychopathologic reactions which occur in schizophrenic and less frequently in manic and depressed patients, subcoma insulin is a useful form of therapy. The psychopathologic reactions which are affected favorably by this treatment are catatonic excitements with marked fear, depression, or elation; acute paranoid reactions with fear, incoherence, elation, or depression; schizophrenic episodes of excessive anxiety; manic excitements with marked anger or sexual excitement; and panic phases in depressive illnesses. Catatonic stupors with marked fear reacted favorably. It should be emphasized that, while many distressing symptoms can be controlled or relieved by insulin, the underlying illness is not necessarily altered.