Somatostatin receptors are activated by somatostatin secreted from nerve and endocrine cells. The Somatostatin Receptors (SSTRs) are expressed in a tissue-specific manner and involved in the regulation of secretion of insulin, glucagon and growth hormone as well as cell growth induced by neuronal excitation in both the central and peripheral nervous systems. Aberrent expression of somatostatin receptors is known in a large number of human tumours. The human medullary thyroid carcinoma cell line TT expresses all SSTR subtypes. SSTR1 has been reported at highest levels in the jejunum and stomach. In addition, this receptor is expressed in adrenal, brain, liver, lung, eye, and pancreas. ESTs from SSTR1 have been isolated from normal placenta and colon cancer libraries. Normal T-cells expressed SSTR1 and SSTR5 while T-cell leukaemia lines do not. Selective activation of SSTR1 inhibits hormone secretion and cell viability in GH- secreting and PRL-secreting adenomas in vitro.