The tetradecapeptide somatostatin is widely distributed in the body in endocrine-like calls and in nervous tissues. When produced in endocrine cells, it seems to inhibit the secretion of hormones at the site of production, for example, it inhibits the secretion of growth hormone in the pituitary gland, insulin and glucagon in the pancreas, and the local hormones in the gastrointestinal tract. Its role in the nervous system is not clear, but it may act as an inhibitory transmitter substance or modulator. As for its mode of action, the data suggest that interference with the levels of cyclic nucleotides, within the cells as well as with Ca++ fluxes may be important. The clinical uses of somatostatin have been explored, especially in diseases characterized by hypersecretion of hormones known to be inhibited by somatostatin. But the wide distribution and multipotent inhibitory action calls for attention. Analogues to somatostatin with specific actions have already been produced and await clinical evaluation.