Natural Somatostatin has a short half-life (3 min), is only active after intravenous administration and causes a rebound hypersecretion of hormones after discontinuation of administration. Recently a long-acting powerful Somatostatin analog was developed (SMS 201-995; Sandostatin) which has a half-life of 113 min after subcutaneous administration. After administration of this analog no rebound hypersecretion of hormones was observed. In the present review the effects of the acute administration and of long-term treatment with SMS 201-995 in acromegalic patients is discussed. In addition the potential role of therapy with Somatostatin analogs and the preliminary effects of Somatostatin and/or SMS 201-995 are discussed in disorders of gastro-intestinal function (haemorrhages, diarrhoea, pancreatitis and endocrine pancreatic tumours), diabetes mellitus, central nervous system disturbances and oncology. Finally, several aspects of the tolerance, tachyphylaxis and side effects of SMS 201-995 are discussed.