Insulin- and gastrin-secreting neuroendocrine tumours of the pancreas are often very small at presentation because of the potent effects of their hormonal outputs, and they may therefore prove difficult to localize preoperatively. This is despite the advances made in recent years in cross-sectional imaging techniques, especially multidetector-row computed tomography and endoscopic ultrasound. In this chapter the techniques of angiography and arterial stimulation venous sampling used for the localization of these neoplasms are described; a combination of these two modalities provides both anatomical and functional data that are not available with other localization techniques, thereby improving operative outcome.