1. Large doses of diethyl stilbestrol were administered to 45 women with involutional psychoses.2. Twenty-seven (60 per cent) were improved, while in a control series of 128 women, only 54 (42 per cent) were improved.3. (A) The simple cases of involutional psychosis responded well to estrogenic therapy. (B) The cases of moderate severity and those of the mixed type reacted favorably, particularly when adjuvant therapy was employed, but relapses occurred and the degree of improvement was not as marked. (C) The psychotic manifestations in the severe cases were not materially affected. These cases may represent a different clinical entity than the mild cases. (D) Therefore, a therapeutic test with estrogenic substance may possess some diagnostic value in involutional psychoses.4. Cases of dementia præcox, manic-depressive psychosis, and chronic psychoneurosis occurring during the involutional period were not favorably influenced by estrogenic therapy.5. Diethyl stilbestrol administered orally was about as effective as alpha estradiol injected intramuscularly. About half of those who were given the former preparation exhibited some form of toxic reaction which for the most part did not seriously interfere with the treatment régime. Both substances produced similar psychologic effects.6. It is concluded that adequate estrogenic therapy has a definite value in the treatment of cases of involutional psychosis of the simple type.Abstract Teaser