The repeated induction of seizures (convulsive therapy) relieves the symptoms of severe depressive mood disorders, particularly those accompanied by vegetative symptoms. Neuroendocrine abnormalities characterize patients with endogenous depression, and the abnormalities are reversed by convulsive therapy. Tests of neuroendocrine functions provide criteria for the classification of such cases, and probably will be useful in defining suitable cases for convulsive therapy. We postulate that the antidepressant efficacy of convulsive therapy results from the increased release and more widespread cerebral distribution of hypothalamic peptides with behavioral effects. Such a hypothesis provides a basis for clinical trials of centrally active peptides in cases of endogenous depression, and for studies of neuroendocrine functions as predictors of outcome in convulsive therapy.