Octreotide is particularly useful in patients with resistant acromegaly and some gastroenteropancreatic (GEP) tumours, e.g. VIPomas, carcinoids and glucagonomas. The efficacy of octreotide can be attributed to its action regarding somatostatin receptors on GEP tumour cells. The symptoms of these tumours are due to a greater extent to the peptides they secrete than to their actual size. In most patients these symptoms improve or disappear completely with octreotide treatment. Side effects of treatment are mainly mild and do not necessitate withdrawal of the treatment. Octreotide is currently the drug of choice for controlling the symptoms of inoperable GEP tumours.