Autonomic Imbalance and the Hypothalamus was first published in 1957.Fundamental alterations in the reactivity of autonomically innervated structures frequently have been observed in physiological tests as well as under clinical conditions. However, the mechanism of these alterations and the changes in the reactivity of the central structures of the autonomic nervous system that are their most frequent site of action had not been subjected to systematic, experimental analysis until Dr. Gellhorn launched the investigations he reports in this volume.The influence of the sino-aortic reflexes on the hypothalamus and the cortex is analyzed experimentally, and new data on the relation of the hypothalamus to vascular, respiratory, and visceral functions are presented. On the basis of his physiological work Dr. Gellhorn shows how clinically applicable methods for the diagnosis of parasympathetic and sympathetic disorders at the hypothalamic level may be devised. He shows the significance of his observations for an understanding of the physiology of the emotions and suggests clinical applications to such problems as hypertension, central autonomic disorders, and functional psychoses. The influence of age on parasympathetic and sympathetic excitability is shown on control subjects and on neuropsychiatric patients, and significant differences between these two groups at similar age levels are disclosed.For the convenience of the clinical reader the experimental results are summarized in a special section before the clinical applications are discussed.