Mood disorders during the postpartum period occur in 10% to 15% of women. The hormonal basis of these disorders, however, has not been investigated systematically and extensively. We review recent studies, primarily from the past 5 years, in which investigators examined the major categories of proposed hormonal etiologies, including gonadal steroids, thyroid hormones, cortisol, prolactin, and melatonin, and then present descriptive statistics of our preliminary findings in these hormonal dimensions from a group of 20 depressed and normal control pregnant and postpartum women.