This chapter has reviewed briefly the neuroanatomy relevant to the synthesis and release of AVP and OXT. Osmoregulation and baroregulation of AVP secretion has been discussed in detail, emphasizing the importance of osmotic control under normal physiological conditions. The remainder of the text has covered the two major pathophysiological disturbances of AVP secretion. In considering diabetes insipidus a pragmatic approach has been taken in the differentiation of the causes of polyuria and its treatment. A similar approach has been applied to the syndrome of inappropriate antidiuresis. Brief mention was made of the function of OXT.