Chronic portal vein cannulation in the rat is an important technique to study secretory rates of hormones from the endocrine pancreas. Moreover, it can be used for studying the effects of enteric hormones and pharmaca on behavioral and physiological processes. This article contains an extensive description of a cannulation technique of the portal vein that has many advantages over those reported so far in the literature, and that was very successful in several behavioral and physiological studies during the last decade. (C) 1999 Elsevier Science Inc.