N eoplastic cells express and often even over-express the somatostatin receptors. It is im portant because the presence o f sst receptors predicts-to some extent-the possibility o f treatm ent with SST analogs. The presence of sst receptors may be examined in vivo by means of the receptor scintigraphy using the radiolabeled SST analogs. The receptors can be also detected in vitro (ex vivo) on surgical or biopsy specimens. Among the in vitro (ex vivo) methods, the immunohistochemical investigation with specific anti-receptor antibodies seems to be particularly useful for routine diagnostics. The chapter discusses the data on the incidence of sstl-5 receptor subtypes in the different human tumors including pituitary adenomas, brain tumors, thyroid and adrenal tumors, neuroendocrine tumors (NET), and nonendocrine cancers. These data lead to the conclusion that the expression of sst recep tors is not restricted to the neuroendocrine and endocrine tumors but can be detected also in nonendocrine malignancies. The above suggests that the latter are also candidates for therapeu tic trials with SST analogs. On the other hand, this possibility is limited by the fact that the detectable sst receptors are not always functional.