There is mounting evidence showing that some pituitary and hypothalamic hormones play an important role in the affective disorders and may directly affect brain function and behavior. This report briefly reviews some recent endocrinological studies in affective illness with special reference to bipolar and unipolar form of illness. Data on prolactin and growth hormone response to levodopa in bipolar and unipolar illness presented. Preliminary data on plasma dopamine beta hydroxylase activity measured over a 24-h period are illustrated in patients suffering from bipolar and unipolar illnesses as compared to controls. The significance of these results is discussed in relation to biogenic amine dysfunction in the major affective disorders.