Updated project metadata. A peptidomic analysis of plasma from patients with well characterised pancreatic neuroendocrine tumours (PNET) was performed. A nano LC-MS analysis identified a number of peptides from the glucagon gene, which were idenfiried in a previous case study using multiple immunoassays. Peptides to other proteins involved in peptide secretion were also identified. Plasma from a second glucagonoma patient was analysed using a high flow approach, and this identified similar peptides to the nano analysis. In order to demonstrate the potential clinical application of LC-MS to characterising neuroendocrine tumours, a large cohort of plasma samples were analysed to demonstrate the ability of this approach to identify glucagonoma patients, and differentiate from a single insulinoma patient