General Aspects of the Biology and Function of Somatostatin.- Molecular Heterogeneity of Somatostatin.- Evolution of Somatostatin Genes and Gene Products.- Anatomical Distribution of Somatostatin Cells.- Somatostatin in the Blood and Other Body Fluids.- Actions of Somatostatin.- Molecular Model of Somatostatin Action.- Regulation of Somatostatin Secretion and Gene Expression.- Physiological Significance of Somatostatin.- Somatostatin in Disease.- References.- Somatostatin Receptors in the Central Nervous System.- Somatostatin Receptors.- Somatostatin Receptors in Pathology.- Conclusion.- References.- Somatostatin in Neuropsychiatric Disorders.- Neuropsychiatric Disease-Related Alterations.- Central Nervous System Effects of Somatostatin.- Somatostatin in Affective Disorder: Clinical Relevance.- Endocrine Correlates.- Role in Seizure Disorders and Effects of Psychopharmacological Agents..- Conclusions.- References.- The Physiological Role of Somatostatin in the Regulation of Nutrient Homeostasis.- Release of Somatostatin.- Mechanisms of Somatostatin Release.- Physiological Effects of Somatostatin.- Somatostatin and Nutrient Entry into the Circulation.- References.- Therapeutic Use of Somatostatin and Octreotide Acetate in Neuroendocrine Tumors.- Pharmacology of Octreotide Acetate.- The Effects of Somatostatin and Octreotide on the Pituitary.- The Effects of Somatostatin and Octreotide on Neuroendocrine Tumors of the Gut.- Unresolved Issues.- References.