SummaryBackground  As there is considerable overlap between the fasting serum gastrin concentrations found in Zollinger–Ellison syndrome and various common conditions such as Helicobacter pylori infection and acid suppressing medication use, establishing the cause of hypergastrinaemia in individual cases can sometimes be difficult.Aim  To review the causes of hypergastrinaemia and the role of additional non‐invasive investigations in hypergastrinaemic patients.Methods  Review of articles following a Pubmed search.Results  As gastrinomas may cause serious complications and be potentially life threatening, investigation of hypergastrinaemic patients should particularly focus on confirming or refuting the diagnosis of Zollinger–Ellison syndrome. Establishing the cause of hypergastrinaemia may be difficult when there is only a mild‐to‐moderate elevation of fasting serum gastrin concentration and concurrent treatment with proton pump inhibitor drugs and the presence of H. pylori infection can both confuse the clinical picture. A variety of provocative tests are therefore useful for establishing whether a hypergastrinaemic patient has a gastrinoma and current evidence suggests that the secretin test should be used first line.Conclusions  We suggest an algorithm for the investigation of patients found to have an elevated fasting serum gastrin concentration and address the roles of gastrin stimulation tests in current clinical practice.