SummaryThe findings in two cases of islet tells pancreatic tumors have been presented. In one case, aortography led to accurate localisation of the tumor before operation. In the other case, biological tests are discussed on a physiopathologicai basis. It seems that insulin production by the tumor is usually not stimulated by glucose but well by leucine. This fact could explain the phenomenon of leucine induced hypoglycemia in insulin secreting adenomas. It is also suggested that the insulin secreting capacity of the remaining non tumoral pancreas is depressed during hyperglycemia and diminished tolerance to glucide could he explained by this mechanism.