Diagnostic test of choice and allows biopsies to be taken. NSAID related ulcers are reguarly located in the antrum and there is limited mucosal thickening or irregularity whereas ulcerated [[Gastric Neoplasia - WikiClinical|gastric tumours]] will have thickened mucosa and edges. Any biopsies should be taken at the edge of normal and diseased to avoid further deepening or perforation.