This review examines proposed endocrine-based etiologies of postpartum depression (PPD) and how knowledge of these etiologies may affect future treatments. It is based on a review of papers shedding light on the etiology of PPD with special emphasis on research into endocrine-related depression. A picture of PPD is starting to emerge that suggests a variety of endocrine root causes as well as psychosocial risk factors. Hormones reviewed include progesterone, estradiol and estriol, cortisol, corticotropin-releasing hormone, prolactin, thyroid-stimulating hormone and triiodothyronine/thyroxine. Other substances examined include 3 antithyroid autoantibodies. Better understanding of the physiologic bases for depressive symptoms may lead to correction of the underlying pathology of PPD rather than treatment of symptoms.