Well-differentiated neuroendocrine tumors (NT) expresses somatostatin receptors (sstr). A composition of sstr subtype determines biological behavior. We therefore evaluated their immunolocalization in 71 NT cases using immunohistochemistry. Sstr immunoreactivity was demonstrated as follows: sstr1 39.4% of all cases, sstr2A 90.1%, sstr2B 39.4%, sstr3 50.7% and sstr5 76.1%. Based on these findings, the effects of the recently developed sstr subtype-specific somatostatin analogue SOM230 on the NT cell line NCI-H727 were examined. SOM230 significantly reduced cell proliferation while the conventional analogue SMS201-995 did not. Therefore, SOM230 has advantages in controlling the cell proliferation of these tumors but the status of sstr subtypes should be determined, possibly using immunohistochemistry, in order to confer its maximum benefits.