Not much is known about the physiology of intraportally transplanted islets. One reason for this is that it is difficult to study such islets, since they are scattered throughout the liver. We employed a perfusion technique to characterize the functional properties of syngeneic intrahepatic 1-month-old islet grafts, and compared them to islets transplanted beneath the kidney capsule, as well as native islets. The cellular composition of the islet grafts was also examined. Glucose and arginine administered through the hepatic artery, but not through the portal vein, induced insulin release from the intraportally implanted islets. Moreover, arginine, only when administered through the hepatic artery, induced glucagon release from the same islets. The first phase of glucose-stimulated insulin release from both islets transplanted to the liver and kidney was delayed, and less prominent when compared to the pancreas. Intraportally transplanted islets contained fewer glucagon-positive cells than islets transplanted to the kidney and native islets. Our findings demonstrate that intraportally transplanted islets respond with insulin and glucagon to secretagogues, but only when stimulated through the hepatic artery. Whether intrahepatic islets may sense other substances than glucose or arginine occurring in high concentrations in the portal vein following intestinal uptake remains to be studied.