Somatostatin, a 14 amino acid peptide hormone, is a potent inhibitor for secretion of gastrointestinal hormones from endocrine cells. The clinical use of somatostatin for treatment of endocrine gastrointestinal tumours was limited due to its short half-life (2-3 min). Octreotide (Sandostatin), a long-acting somatostatin analogue, has been developed for subcutaneous use with an elimination half-life of about 45 min. This offers a new way of long-term treatment for patients with endocrine gastrointestinal tumours. The effect of octreotide in various forms of these diseases and its importance for the possible inhibition of tumour growth are described.